On Amazon, you don't know which seller's goods are being shipped to you, if it's "fulfilled by Amazon" or from Amazon directly.

So if two sellers are selling the same item, with the same exact SKU, and both send their inventory to Amazon to be warehoused and shipped, Amazon will happily send you either seller's item, depending on which is more convenient to send. (Perhaps seller A's stuff is in a warehouse closer to you.) This sounds good in theory, because all those products are identical, right? What if seller B's products are all counterfeit? So you buy from seller A who you think is legit (and for the example is), but you get seller B's fake crap, and seller A was powerless to stop it.