Someone at Amazon had to have looked at the sales boost fake reviews give and decided to leave them. There is just no way that this hasn't been tested. So if the fake reviews sales increase > decrease in user retention, they decided just let the crap fly. This has probably been concluded more than once.

It is too bad. Ironically eBay used to be the place all the random crap ended up, now when I order something off eBay I expect it to show up in better shape than from Amazon. Amazon turned in to the flea market of the web.