I was thinking the exact same thing the other day when I was listening to NPRs Antitrust series. The talk about this for a bit but the main difference is that Amazon pitches itself as a platform/portal. Essentially any company can it as medium to sell things. It's anti consumer since they are now selling their own brand while promoting it on this so called portal. Costco on the other hand is a whole seller. Companies work with contracts and agreements with Costco to arrange for the selling goods. On top if that, Costco does not explcity promote their goods. If you look at salts, they are equally placed for you to select and the customer can decide themselves.