My short answer: when traffic looks healthy but growth has stalled, I want to find the biggest commercial bottleneck before changing anything. It may be the storefront. It may also be product data, merchandising, availability or the traffic mix.
My ecommerce background makes me wary of diagnosing everything as a design problem. A beautiful product page cannot compensate for customers being sent to the wrong products or Google receiving weak information.
Can customers find the right product?
I start with navigation, search, categories, filters and sorting. If discovery is hard, the customer may never reach the product page everyone wants to optimise.
Does the product page answer the buying questions?
Images, condition, options, delivery, returns, compatibility, stock, trust and price context matter. On mobile, the order and density of this information matter even more.
What information is being sent to Google?
Titles, product types, identifiers, availability and price affect how product listings are understood. Feed and Merchant Center work sounds technical, but in plain English it is about making sure Google receives accurate, useful product information.
Where does checkout create doubt?
Unexpected costs, weak delivery information, forced account creation or an awkward payment journey can undo everything earlier in the funnel. I review the complete purchase journey rather than one template in isolation.
Apply the principle to your own business.
If the issue is your website and you are unsure whether to repair or rebuild, start with the free Website Rescue Review. If the problem is broader, send me the business and what is not working.