Ask to see a redesign, not just launches. Building on an empty store is the easy version. A redesign means working around live orders, existing URLs, installed apps and a team that keeps editing products mid-project. Ask for one store they rebuilt while it kept trading, and what they had to fix in the first month after launch.
Get the scope written as templates, not pages. Shopify themes run on templates: home, collection, product, cart, page and blog post, plus any alternate templates you use for landing pages or special products. "Twelve pages" tells you nothing. A list of which templates get rebuilt, which sections are new and which stay as they are can be compared quote against quote.
Ask how they handle the switch. The right answer is building on an unpublished theme, reviewing it in preview, then publishing in a quiet trading window. Ask who re-adds app blocks and embeds, who re-tests tracking and who owns the redirect list if any handles change. A developer who plans to work on the live theme is a red flag.
Ask what happens to your existing code edits. Custom code stays behind when you change theme. Every hard-coded tweak, custom snippet and metafield-driven section has to be found, then rebuilt or retired. A good developer audits this before quoting. A weak one finds it in week three and sends a change request.
Ask who tests, and on what. A redesign should be tested on real phones with real checkout journeys: a discount code, a gift card, a subscription product if you sell them, and every payment method you offer. Designers rarely test the cart, and the cart is where redesign launches tend to break.
Red flags. A fixed price before anyone has looked at your theme code and app list. No mention of redirects, analytics or app blocks. A plan to rebuild everything when two templates cause most of the problems.