Comment by mikeash

There’s a huge and fundamental difference between what you describe and what Amazon is doing. What you describe involves both A and B. A is figuratively putting their name on the product, and they have an incentive to make sure that everything is above board. You are getting it from A, by way of B.

The way Amazon does it, A isn’t involved in the choice of who supplies the product, they just receive the money. They don’t even know who supplied the product, if I understand things correctly. You’re just buying from B, while Amazon says you’re buying from A.