Sabii had been on BigCommerce for 3 years. The platform worked, but two specific pain points had become blockers to growth.

First, the subscription quiz. Sabii sells customized wellness subscription boxes. New customers take a 6-question quiz to determine which box variant fits their needs. On BigCommerce, the quiz had been built as a custom page using their Stencil framework, then handed off to checkout via URL parameters. The quiz worked, but the experience was clunky: customers would complete the quiz, see a generic add-to-cart screen, and then go through standard checkout. Quiz completion was 38%; cart-to-purchase from quiz was 14%.

Second, the gift-with-purchase logic. Sabii runs frequent GWP promotions (e.g., spend $80, get a free travel-size product). BigCommerce's native promotion engine could handle simple GWP rules but struggled with conditional logic like free product depends on which subscription tier the customer chose in the quiz. This required workarounds that broke periodically.

Priya, Sabii's CEO, reached out in February 2025. Her ask was specific: We need a checkout flow that handles quiz logic and GWP rules natively, on mobile, without me filing a ticket every time something breaks.

We did the free 30-minute audit and immediately saw two possible paths.

Path A: Stay on BigCommerce. Build a custom checkout app using BigCommerce's Checkout SDK. Feasible but expensive — BigCommerce checkout customization is significantly harder than Shopify's, and Sabii would be locked into a platform they'd already outgrown for other reasons.

Path B: Migrate to Shopify. Build the quiz and GWP logic into the storefront cleanly. Shopify's checkout extensibility (on Plus) is officially supported and simpler to customize. Cost would be similar to Path A, but the foundation would be on a platform with more headroom.

We recommended Path B. Priya wasn't looking for the cheapest option — she was looking for the path that didn't leave her with the same problem in 18 months. Proposal: $24,000 fixed, 4 weeks, including the custom checkout work.

Week 2 was the standard migration work: BigCommerce data export, Shopify import, custom theme rebuild on a Dawn fork. The BigCommerce data was clean (cleaner than most migrations we do), so the migration itself was quick. Most of the week went into theme work.

Week 3 was the custom checkout. We built the subscription quiz as a Shopify Custom Section that lives on a dedicated page (/quiz). The quiz logic is in JavaScript, with results saved to a customer metafield. When the customer adds to cart, the cart drawer reads the metafield and applies the right product variant + any conditional GWP automatically.

The GWP logic uses Shopify's Cart Transform API (available on Plus). When the cart total + quiz metafield meet specific conditions, the API automatically adds a free product variant with a 100% discount line item. No third-party apps. No timer-based scripts. The customer sees the free product appear in cart in real-time, and it can't be removed (because it's tied to the cart transform).

The interesting design challenge: how to communicate the GWP qualification to customers BEFORE they hit the threshold. We built a small progress bar component that lives in the cart drawer: Spend $12 more to unlock your free travel-size. It updates in real time as items are added or removed. This was actually the highest-impact piece of the whole project for conversion — it lifted average order value by $11 once it launched.

The launch went smoothly. DNS cutover took 5 minutes. The first issue we hit was a small one: the quiz's metafield wasn't syncing to one customer cohort (people who'd been on the site as guests before the quiz launched). Fixed in 20 minutes with a one-line Liquid filter.

The bigger surprise came on day 3. We'd expected the quiz completion rate to stay roughly flat with the BigCommerce baseline (38%). Instead, it jumped to 54% within the first week. The new flow — quiz → personalized add-to-cart → instant GWP qualification feedback — felt more like a guided shopping experience and less like filling out a form.

By day 30, quiz completion was holding at 54%, and cart-to-purchase from quiz had moved from 14% to 20%. The compounding effect on subscription revenue was significant.

The biggest lesson from this project was about scope discipline. The original proposal was 4 weeks, $24K. We finished in 3.5 weeks, but Priya kept asking small while you're in there questions — could we also rebuild the account page? Add a referral program? Set up a new Klaviyo flow?

We said yes to one (rebuilding the account page, since it was thematically connected to the quiz work) and no to the others. They went on a list for a future engagement. This was harder than it sounds — every no felt like leaving money on the table. But protecting the fixed-scope, fixed-timeline promise mattered more than absorbing one more project into the existing one. Sabii later booked a 3-month retainer that covered the rest of the wish list.

If we ran this project again, we'd build the GWP progress bar earlier in the sprint. We built it in week 3 as part of the cart drawer work, but it was probably the highest-leverage component of the entire engagement. Future projects with similar GWP mechanics: progress bar in week 1, refine in week 2, integrate in week 3.