There is not much to wonder about, Amazon does it because it critical to their fulfillment service, one of the key ways amazon makes money and keeps it 1-2 day delivery times is inventory mixing, i.e if you order from Seller X, you may actually get Stock that Seller Y shipped in.
This is why they need to merge listings into 1. It is also why there is soo much fraud on Amazon, and I dont believe they will ever fix it, the logistic costs would make Fulfilled by Amazon unprofitable if they had to stop mixing stock
If they use the Fufilled By Amazon service, which if you want to have "Prime" shipping you have to, then yes that is possible and more common than it should
The way the service works, is that you the vendor will ship your products into a amazon warehouse, other vendors will ship the "same items" a amazon warehouse, all of these "same items" are mixed together in the inventory system, your account is has a credit of "X items" but not the specific items you shipped in to the warehouse
Example
Acme Vendor shipped to amazon 15 Logitech MX Mouses
When amazon gets the mouses it take all 30 and puts them in a big box, as the orders are filled even if you ordered from Acme, you make get one of the one Evil shipped into Amazon
I think there’s a discount if you allow commingled inventory (or a cost to keep it separate) which makes sense as Amazon has to track and potentially stock it in multiple warehouses
The comingled inventory actually is a good idea, just flawed. Go ahead, comingle the inventory but keep track of where each item came from so when the counterfeit is discovered they know where it really came from and don't blame the innocent supplier.
Amazon taking action against the vendor, and consumers blaming the wrong vendor.
When you order from Amazon Marketplace you can clearly see who you are ordering from, even if Amazon shipping the item. Consumers getting a bad product will then no only review the item but the seller with negative feedback even though the seller they bought it from may have done nothing wrong
That's what amuses me - what, it requires a few additional characters on the stock barcode?
Of course the real problem is the counterfeiters have no problem starting a new vendor every few weeks or even days, so the damage may already be done by the time the reports come back.
This is why they need to merge listings into 1. It is also why there is soo much fraud on Amazon, and I dont believe they will ever fix it, the logistic costs would make Fulfilled by Amazon unprofitable if they had to stop mixing stock