Amazon used to have a webpage that clearly stated they commingle inventory from all sellers, so it has long been public information that when you buy something on Amazon.com, the seller you buy from does not matter.
I also assume the reason Amazon commingles is it makes their 2 day shipping promise cheaper or more possible to fulfill. If seller A’s items are on the east coast, and seller B’s items are on the west coast, and the items are identical, then it makes sense to send you the closest one.
Obviously, the problem is items are not identical, and quality control is not something I am interested in doing as a customer of Amazon’s.
If you order real stuff, and get fake stuff, then it matters.