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
Evil Vendor shipped Amazon 15 Counterfeit 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
