You'll get a private page showing their stack, where the build is underbuilt, and the four things I'd ship to fix it — with the actual code, ready to paste.
I read what's visible on the storefront — apps detected, theme, currency, product range, the collections they expose, and any subscription / wholesale signals. No login, no admin access.
Then I sketch where the stack looks light and write the actual code for what I'd ship. It's a real reference for your dev, not a sales deck.