This happens because Amazon allows inventory commingling. For example Amazon has their own, legitimate inventory in a West Coast warehouse, and a third party seller has the same inventory with the original UPC manufacturer bar code on it, sitting in an East Coast warehouse. Amazon considers this 1:1 inventory. Amazon will debit their inventory on the West Coast, and credit the inventory that belongs to the third part…
This is sadly so true. I have stopped using Amazon after 15 years due to the unacceptably high rate of counterfeit, grey market or used items I got on a daily basis. It's totally insane. I have even emailed Jeff Bezos and got into the trouble of talking to all middle managers. They don't care.
Months back I ordered some Miele vacuum bags and they too were counterfeit.
I had never experienced this until 2019.