Storetasker Vetted Expert · Fiverr Pro

Shopify CRO and development for brands whose numbers need to be right

German Shopify developer and CRO specialist, 16+ years in frontend, 5+ exclusively on Shopify. I find where your store loses orders, fix the tracking that hides it, and build the changes myself — in the theme, measured before and after.

Book a 20-min intro call View work
Sebastian Käufer at his desk, Shopify code on the screen behind him

Sebastian Käufer

You talk to me directly, no account manager.

16+ Years Experience
580+ 5-Star Reviews
300+ Clients
Working from the Yucatán jungle — German precision, Yucatán calm

Selected Work

Recent Shopify projects

Conversion work with the numbers behind it, plus the themes, product pages and storefront features it runs on. Three projects in detail, the rest at a glance.

In detail

Chart from the delivered read-out: Hat product page mobile add-to-cart rate 1.95% before, 5.08% after the redesign, +161%

CRO retainer · Mobile PDP rebuild · Nicebeam

Mobile add-to-cart rate on the top-traffic product page from 1.95% to 5.08% in 28 days

CRO Mobile PDP Measured
Brief
The store's highest-traffic product page was also its weakest converter. On an iPhone the add-to-cart button sat below the fold, 85% of visitors never scrolled that far, and the most-tapped element on the page was the close button of a newsletter popup.
Built
Rebuilt the mobile first viewport: quantity and add-to-cart on one row above the fold, details open by default, spec icons moved down. Popup switched from on-load to 40% scroll depth store-wide. Shipped as a reversible template, measured on a 14-day cadence against a matched baseline.
Result
Mobile add-to-cart 1.95% → 5.08% (+161%), channel-controlled 3.66% → 10.31%, while the two product pages that were not touched stayed flat. Store-wide session-to-order rate 0.69% → 1.04% on flat traffic in the first month. Reported as directional, not as proof — and that is how I report it to you.
Studio.tools B2B Shopify theme, product page with spec sheet

Custom theme on Horizon · B2B · Switzerland

A B2B store with prices and checkout gated behind a customer tag

Horizon B2B Logic Customer Accounts
Brief
Swiss furniture maker selling meeting-room systems to companies. Wanted an ultra-minimal storefront where prices and checkout only exist for approved business customers, without an access-control app.
Built
Built on Shopify's Horizon theme and reduced to the essentials: sidebar navigation, horizontal product scroll, spec sheet per product. Access gating in Liquid via customer tags, passwordless login on Shopify's new customer accounts, email validation on the access request, error logging through a Cloudflare worker.
Result
One theme, no page builder, no access app. Access rules are settings in the theme editor, so the client changes them without a developer.
Zimply Natural product page with bundle pricing and pharmacy trust badges

Migration · Custom UI on Concept · Germany

WordPress and a custom Vue.js storefront moved to Shopify on a three-week schedule

Migration Bundle Pricing Multilingual
Brief
German natural-pharmacy brand selling individual remedies through partner pharmacies. The old stack (WordPress plus a hand-built Vue.js storefront) was hard to maintain and harder to extend.
Built
Migration to Shopify with a completely custom UI, built on the Concept theme as the base and carrying the brand's CI throughout. Homepage, product page and blog rebuilt; the PDP with bundle pricing, pharmacy trust badges and a medical advisory board section. Since launch: multilingual setup with 7,800+ translated entries and localised landing pages.
Result
Fixed-price build, then a retainer. The brand kept me on for ongoing development; the theme now ships from a GitHub repo in their own organisation.

More projects

Excerpt of the delivered audit: 1 GA4 property, 0 custom pixels, Meta match quality 8.8, purchase counted twice in Google Ads

Tracking audit · YouChews

Every sale counted twice in Google Ads

2×

Tracking audit — one real error behind a paused ad account

Google had flagged the account and paused campaigns. Live network captures, a theme tag scan and a GA4-vs-Shopify reconciliation showed clean on-site tracking and one real error: two Primary purchase conversions in Google Ads. Fixed the same day, confirmed.

GA4 Google Ads Meta CAPI
Excerpt of the delivered Measurement & Tracking Audit, Month 1 read-out

Tracking consolidation · Nicebeam

GA4 properties collecting the same traffic

4 1

Tracking consolidation — four GA4 properties down to one

Four properties collected in parallel, an expired server-side GTM certificate was silently losing GA4 and Ads conversions, and an Ads purchase conversion fired on every page load. Mapped with live captures, cleaned up with the client's ads team, verified after every step.

GA4 GTM Verification
Cover of the delivered Puflow conversion audit, 13 August 2026

Conversion audit · Puflow

Findings, 5 critical, every number with a dated capture

12

Conversion audit — twelve findings and the honest part

Fixed-price audit of the full funnel: cart trust placement, delivery info, a three-part tracking gap, popup intrusion, the buying case below the fold on the PDP. Plus what an audit owes you: price position and delivery time named as the biggest constraints, even though they are not website problems.

Funnel Audit Evidence Verification Review
Header of the delivered results report: Core Web Vitals passed, main-thread blocking −32%, Lighthouse 47 to 54, ads conversion data fixed

Mobile speed sprints · YouChews

Total blocking time on the homepage; Core Web Vitals passed on real users

−33%

Mobile speed sprints — Core Web Vitals passed in three sprints

The hero image sat fully downloaded but invisible for up to 15 seconds on mid-range phones, stuck behind marketing tags. Three sprints on a draft theme: image priority and script order, two unused apps removed, 1.19 MB of dead app code deleted. Field data green: LCP 1.6 s, INP 104 ms, CLS 0.

Core Web Vitals Tag Diet Measured
Duostep athletic socks custom Shopify theme

Duostep — Athletic socks theme

Athletic sock brand positioned on engineering rather than fashion. Custom theme with an editorial layout, engineering sections and a three-level product structure.

Custom Theme Editorial Layout Product Architecture
↗
Panoptic luxury eyewear

Panoptic — Vintage eyewear storefront

Luxury vintage eyewear brand with a story to tell. Editorial, mobile-first storefront that puts brand storytelling ahead of the catalogue.

Editorial Layout Storytelling Sections Mobile UX
↗
Magniflex premium mattress store

Magniflex — Mattress product page

Premium mattress brand with a complex product range. Custom product page with Liquid-driven variant logic, built around the purchase decision.

Custom Product Page Variant Logic Liquid
↗
Barkle kit selector with subscription option

Barkle — Subscribe & save selector

Supplement kit sold in quantity tiers and on subscription. Kit selector with tier savings and one-time vs. subscribe & save, built as a theme section.

Subscription Logic Quantity Tiers Custom Section
↗
Auora lingerie size guide

Auora — Lingerie size guide

Lingerie store where fit is the main purchase barrier. Custom size guide tables and product UX built directly into the theme.

Size Guide Custom Tables Product UX
↗
OvaTime fitness supplement store

OvaTime — Nutritional tables

German supplement store with detailed nutritional data per product. Dynamic nutritional tables driven from product data, no hand-built HTML per product.

Nutritional Tables Product Data Custom Liquid
↗
Sultan of Style cart drawer with free shipping bar and limited offers

Sultan of Style — Cart drawer with tiered offers

Perfume brand running stacked promotions at once. Cart drawer with free-shipping progress, per-item limited offers and tier discounts calculated in the cart.

Cart Drawer Discount Logic Free-Shipping Bar
↗
PureStream free gift system

PureStream — Automatic free gift system

The store wanted to reward orders without manual discount codes. Free-gift system on the Cart API that adds and discounts the gift based on cart contents.

Cart API Gift Logic Auto Discount
↗
Körper health landing page design

Körper — Health landing page

Long-form landing page for a health brand: problem, method and product in one scroll. Designed and built to a best-practice landing page structure.

Landing Page Custom Sections Long-form Layout
↗
Mosquito King single-product landing page

Mosquito King — Product landing page

Single-product brand that needed one page to do all the selling. Dark, high-contrast landing page with pack selection and a problem-to-solution story.

Landing Page Pack Selector Single Product
↗
OvaTime landing page

OvaTime — Landing page

Dedicated landing page for a supplement brand. Dark UI, mobile-first, built directly in the theme instead of a page builder.

Landing Page Custom Section Theme-native
↗
Lotus product comparison

Lotus Hygiene — Product comparison tool

Hygiene systems brand with a range that is hard to compare at a glance. Interactive comparison tool with feature matrix and integrated reviews.

Comparison Tool Feature Matrix Reviews
↗
The Carpits filterable track comparison grid

The Carpits — Track comparison grid

Carpet race tracks with many variants that are hard to compare. Filterable comparison grid with track specs, skill level and colour options.

Filtering Comparison Grid Product Specs
↗
Asal recipe platform

Asal — Recipe & ingredient platform

Food brand that sells ingredients through recipes. Recipe platform with portion calculator, built in custom Liquid on top of the store.

Recipe Platform Portion Calculator Custom Liquid
↗

Have a similar project?

Book a call

Services

What I take on

01

CRO audit & implementation

Funnel audit on your real data: GA4, session recordings, live checks on a phone. Prioritised findings with dated evidence, then I implement them in your theme and measure before and after against a matched baseline.

Funnel Audit Implementation Before / After
02

Tracking health check

GA4, Google Ads, Meta Pixel + Conversions API, Shopify pixels and consent, checked end to end with live network captures and a GA4-vs-Shopify order reconciliation. Does every sale count once? Report with findings and a fix list.

GA4 Google Ads Meta CAPI
03

Landing pages & PDPs that sell

Conversion-led product and landing pages built in the theme, not in a page builder: buy block in the first viewport, bundle and subscription pricing, trust where the decision happens.

Mobile PDP Landing Page Bundles
04

Custom theme builds

Full themes from scratch or deep modifications of existing ones. Mobile-first, fast, built on Online Store 2.0 architecture with metaobjects where it makes sense.

Online Store 2.0 Performance Shopify Plus
05

Complex Liquid & JavaScript

Product builders, B2B logic, dynamic pricing, cart and checkout customisation, Storefront API work.

Storefront API Cart & Checkout B2B
06

Ongoing development

Retainer or hourly for brands that need a senior developer on call. Also fully branded Klaviyo flows — welcome, abandoned cart, post-purchase — designed and built to match your theme, as an add-on or on their own.

App Integration Klaviyo Flows Maintenance

Best fit: scoped projects and ongoing engagements. For small one-off fixes, the marketplaces mentioned in the FAQ are the faster route.

Process

How a project runs

01

Intro call (20 min)

You walk me through the store and the goal. I tell you on the call whether it's a fit and what I'd need to scope it.

02

Scope & fixed quote

For builds and audits you get a written scope with a fixed price. Ongoing work runs hourly with weekly summaries.

03

Build, review, launch

Milestones on a staging theme, your review at each one, launch when you sign off. Invoiced directly, no marketplace fees.

Ready when you are.

Start with the intro call

Reviews

What clients say

I am convinced this guy is a magician of Shopify because we tried to solve a problem for 7 hours (and we're devs ourselves) and he solved in 30 minutes. Thanks so much for your skills!
Gonmra
China · via Fiverr
We made a complete new theme, based on Dawn. I gave Sebastian a lot of different 'conversion' templates and he made it so perfect that I am really speechless! Very calm, polite and solution oriented.
Mik
Germany · via Fiverr
Outstanding Shopify Coding Service! The work was delivered super fast, highly professional, and tailored exactly to my needs. Communication was smooth and every detail was perfectly handled.
Philipp
Switzerland · via Fiverr
Sebastian exceeded expectations in maintaining my website with unparalleled professionalism and meticulous attention to detail. His dedication shone through as he went above and beyond.
HAKIN
Singapore · via Fiverr

All quotes are public, verified purchase reviews. Read all 580+ on Fiverr ↗

Sebastian Käufer

Beyond the code

Born and raised in Germany, with 10+ years in corporate frontend before going independent as a freelance Shopify developer. I traded the office for the Yucatán jungle, where I run a cenote and campground with my partner. Development is the full-time job; the cenote is what happens around it.

When I'm not coding, you'll find me on off-grid projects, in the garden, or enjoying the slower pace of rural life. This balance keeps my work focused and my perspective grounded.

Top 3% on Storetasker

Hand-selected from 15,000+ reviewed developers into Storetasker's curated expert network.

Vetted Fiverr Pro

Top Rated seller: 313 clients, 798 orders, 580+ five-star reviews.

International Clients

Statement Clothing, LeftLane, Studio.tools, and brands across Germany, USA, Singapore, and more.

FAQ

Before you book

Where are you based and when are you available?
Yucatán, Mexico (CST / UTC-6). Overlap with EU afternoons and the full US working day. Calls are booked through the calendar link; async work runs on your timezone.

How do you charge?
Fixed price for scoped builds and audits, hourly for ongoing development. Invoiced directly. No marketplace fees on direct projects.

Is my project big enough?
If it needs scoping — a build, an audit, a custom feature, ongoing work — yes. For a single small fix, the marketplaces below are the faster route and I'm happy to take it there.

What don't you do?
Public Shopify app development, WordPress / Joomla sites, pure SEO or ad-management retainers, and design-only work without implementation.

What does a tracking health check include?
GA4, Google Ads, Meta Pixel and Conversions API, Shopify pixels and consent, checked with live network captures on the storefront and a GA4-vs-Shopify order reconciliation. You get a report with findings and a fix list; fixes are quoted separately, so the diagnosis stays independent of the sale.

Do you run A/B tests?
Only when the traffic supports one. At a few hundred mobile sessions a day a single test takes months to read, so there I ship the change on a reversible template, measure before and after against a matched baseline, and report it as directional rather than proof.

Do you work with agencies?
Yes, as a white-label senior Shopify developer on project basis.

Do you work in German?
Yes. German or English, whichever your team prefers — calls, documentation and handover included.

Prefer working through a vetted marketplace?
You'll also find me on Storetasker and Fiverr.

Sebastian Käufer · You talk to me directly, no account manager.

Let's build
something great

Book a 20-minute call. You'll know by the end of it whether I'm the right fit, and I'll tell you if I'm not.

Book a 20-min intro call

or email sebastian.kaeufer@protonmail.com

Book a call