If I started using FBA and supplying an item, it’ll go in the same box and chances are more likely an “sold by amazon.com” will sell my product, and I’ll sell an “amazon.com” product.
See the problem?
No they don't. Google 'random stow' and you'll find articles about how Amazon stores incoming items. They are stowed somewhat randomly, but scanned as they are stowed. So the system knows where to find each unit again, and can use that to optimize picking paths.
I was commenting only because most people make the same false assumption (that all units of X in warehouse Y are stored together) and find the random stow model interesting when told about it.
You are referring to mingled inventory which the seller has to opt into explicitly when they decide how to sell their product.
This is not the default, and in my experience, very few sellers choose this option. Most of the inventory is labeled with Amazon-proprietary bar codes that identify the seller.
Amazon could easily solve this problem but they've decided it's more profitable to let it fester. Whether or not it's a good decision in the long run, the same way Sears permanently ruined their reputation by selling shit through their established in-house brands, remains to be seen.
They don't necessarily. Amazon combines items from different sellers together in their warehouses, and doesn't sort them out when picking orders to ship. So if I send them a high quality doohickey to sell with FBA, a customer who orders my doohickey might actually receive Mr. Cheapo's knock-off doohickey because as far as Amazon is concerned they're the same thing and got placed in the same bin in the warehouse.
Sellers can opt out of this but then Amazon charges them more.
The fact that Joe Q Public can make a marketplace account, ship a crate of counterfeit stuff, and have that be sold to buyers of “amazon.com” is absurd and explains the counterfeit problem.