As an Amazon seller, I can confirm that they have tracking linked to each seller. Their system does this via their FNSKU (fullfillment network stock keeping unit) and that is unique to each seller for each product. So if I want to sell a product, that product has an ASIN that defines it specifically and then any seller in the Amazon system that wants to sell that product needs their own FNSKU that applies only to that ASIN. Those FNSKUs are tagged on the items. If you've ever bought third party stuff on Amazon, the numbers are also 10 digits long just like ASINs but they usually begin with an X. FNSKUs can also match the ASIN and that is usually given to the seller that creates the listing so that seller has FNSKU=ASIN. So if you buy private label stuff that is their own branded stuff that no one else sells, it just looks like the ASIN and you probably ignored it. But if you buy a big brand name product like Nintendo, Star Wars, or anything with multiple sellers that sell via FBA/prime, you'll probably see the FNSKU beginning with X.
EDIT - in case it wasn't obvious, Amazon uses the FNSKU barcode for fullfilling their orders. They might have 10 sellers with the same ASIN in that specific warehouse, so the Amazon employees fullfill via FNSKU in those cases, which is why they would require the FBA/prime items in their warehouse to be tagged with the FNSKU to identify which seller owns that exact item vs all the others that also have stock in that warehouse and perhaps even in that exact same shelf/bin.
Apologies if I’m misunderstanding, but are you implying that amazon doesn’t commingle products? Allegedly this is the reason that you can order a “sold by amazon” product but still receive a counterfeit item (likely provides by a 3rd party seller).
No, when they get the product shipped in they stick a seller-specific label on it, then commingle it. When I order an Xbox an employee goes to the Xbox bin, picks any of them and scans it out of the system. Amazon now knows which one I got and where it came from, because the barcode identifies it as originating from seller X. If I complain to Amazon or send it back they can now look up what they shipped me and see if some seller consistently ships them bad product.
In essence commingling prevents you from efficiently grabbing something from a specific seller, but it doesn't prevent you from knowing which one you grabbed.
If the unit has an UPC barcode, the unit is commingled (also called "stickerless" inventory). Commingling means Amazon can use one seller's inventory to fulfill another's order - the units are never stored in the same bin to allow tracking origin.
If the unit has an Amazon seller-specific FNSKU barcode, the unit is not commingled.
The used barcode type can be configured by the seller.
The barcode configuration option does not mention commingling at all (but help pages do), so I can understand some sellers getting confused on whether they are affected by commingling or not.
If there are 25 widgets in a particular bin in an FC, I have serious doubts that the instruction and expectation of the picker is to pick the specific one that has this particular FNSKU.
If they want that behavior, it would seem far better (less error prone and faster) to segregate by FNSKU such that any one location has only one FNSKU for a given ASIN. (That they don’t do this [or didn’t always do this] seems to be the root of how you could get a counterfeit good from a “legit” seller, including Amazon.)
AFAIK they have always segregated different FNSKUs to separate bins for comingled inventory.
The reason you get counterfeit goods is that Amazon prefers to fulfill an order from warehouse A but seller 1 only has units in warehouse B. Seller 2 has units in warehouse A so Amazon performs an item swap between the sellers to save on shipping (or to improve shipping speed).
EDIT - in case it wasn't obvious, Amazon uses the FNSKU barcode for fullfilling their orders. They might have 10 sellers with the same ASIN in that specific warehouse, so the Amazon employees fullfill via FNSKU in those cases, which is why they would require the FBA/prime items in their warehouse to be tagged with the FNSKU to identify which seller owns that exact item vs all the others that also have stock in that warehouse and perhaps even in that exact same shelf/bin.