I've heard that books also have a high counterfeiting rate on Amazon. Over lunch with Paul Horowitz a couple of years ago he mentioned that he's had to fight to get counterfeits of "The Art of Electronics" taken down.

I read on here a while back about FBA inventory getting comingled, but I'm unclear on whether Amazon's own inventory gets comingled as well. Anecdotally I haven't received a counterfeit of anything shipped and sold by Amazon.

I'm not sure about the US situation but you can't be sure even with books: The scientific publisher Springer switched to a print on demand model. This is generally fine but Amazon apparently prints those books themselves after ordering (it says so on the last page) and both printing and binding are of abysmal quality, much worse than what you get elsewhere for the same price.