>All it has to do is conduct an investigation to confirm the complaint, which is as easy as ordering the item in question and confirming it contains the offer reported by a single customer.

The number of humans available to perform daily investigations versus the total number of products sold makes this most decidedly not "easy".

The easiest thing to do here would be to simply return the item because the seller crossed your personal ethical line, and state that as the reason. A large number of returns on an item will definitely get the sellers and Amazon's attention.