"A rating". Why not give high-margin items get a cherrypicked high rating, and low-margin items a cherrypicked three/four star rating (you can't just say everything is five stars, of course).
Possibly, but given (1) everything in the store is highly rated and (2) they're as much as asking customers to "showroom" and check for more information on Amazon.com, it seems like that would backfire pretty quickly.