Do they really? That's horrible! It would also explain so much bad/strange behavior where Amazon gets caught selling fraudulent merchandise.
For a good example of this, look up reviews on CR2032 coin cell batteries sometime. In a nutshell, regardless of which brand you pick or who you buy from on Amazon, it seems you're very likely to get re-packaged and possibly counterfeit goods.
Doesn't Amazon use shared inventory between first party and fulfilled-by-Amazon third party sellers, so that the first party market is potentially as much a hive of scum and piracy as the third party market. I'm quite sure that's been raised as an issue many times with regard to counterfeits.