Alternately, how does the picker know which item on the shelf to select to ensure they have selected the right seller's unit? Look at how amazon stores books in their warehouses:
https://www.google.com/search?q=amazon+warehouse+books&sourc...
Without a label on the book, how do they know which copy to pull from the shelf and put in the box?
I know Amazon says they track inventory, but prime shipped and sold-by-amazon.com boardgames arrive as counterfeits pretty regularly in the board game industry. You can find plenty of reports, with detailed pictures and manufacturer confirmation on BGG. There has to be something going on here, even if it may be more complicated than Amazon is commingling counterfeit and genuine articles.
It's very simple: they're stored in different locations. If seller A is on shelf B, and seller C is on shelf D, then even though the individual items are identical, if you pick up a unit on shelf D you know it's from seller B.
They don't store identical products from different sellers next to each other.
I agree there's a counterfeit issue. Amazon agrees there's an issue, and actually has it as a risk factor in their financial reports. But commingling isn't a significant contributor to it.
You can check if the location it was supposed to be in is empty. From my understanding, the main issues happen during receiving; if it's received to the wrong shipment it'll be incorrectly marked in the system and unlikely to be fixed. Once it's received to the correct system everything else is fairly robust.
>If an item is pulled incorrectly, and then set on the return-to-stock pile, you have no idea where to put it.
If it's pulled, then there'd be a record of where it was pulled from, and that place would be empty.
I've sold millions on Amazon and am friends with many sellers who've collectively sold at least hundreds of millions. I've heard many people with issues with inauthentic complaints. I've never heard of one that can be traced back to commingling.
I've dealt with phantom inventory many times. The correct thing to do is report it. It doesn't always get fixed. The fact that they occasionally have stranded inventory and assign it to a seller doesn't mean they don't generally track transfers of manufacturer barcode inventory, like they say they do. They never claim inventory receiving is perfect. They do claim they track the original source of sales, and there's no reason to think it's not true.