It's a minefield for buyers as well. I have ordered products from Amazon's web site for many years, probably more than 15. Recently, I am getting reluctant to buy because there are so many counterfeit products.
As an example, I wanted to by a genuine Lenovo charger for my X230 laptop. If you want to share my pain, try finding the real McCoy on Amazon.com. I also had to replace my keyboard. That was even worse than the chargers. The products say they are manufactured by Lenovo but they are clearly not. In the end, I suspect the keyboard and charger I got (which I paid quite a bit more than the clearly fake items) are still fakes. They have Lenovo's brand marks on them but they don't look exactly like the originals.
Another good example of counterfeits are cell phone batteries. I tried to buy a replacement battery for a Nexus phone. I had to give up because wading through the endless listings of counterfeit products is just too time consuming.
I don't think Amazon is doing nearly enough to stop this.