In the pre-Internet world there would be someone at the store who would a) do a checkout of the product prior to listing and b) evaluate customer returns and act upon them, in order to protect the integrity of the store. Delivering crap would lead to consequences (in the worst case de-listing) for the vendor.

Amazon doesn't do either - sellers are allowed to put up basically everything that's legal to sell somewhere on the world (including propaganda materials for all kinds of questionable groups including right-wing terrorism), and they don't care at all about complaints from customers about fake products or shoddy quality.

They only seem to care when big media representatives short-circuit the system and raise a stink at the PR team.