A good friend of mine quit selling on Amazon because, as he put it "I didn't sign-up to compete with the Mafia".
Among the long list of issues he rattles off during a conversation are things like fake reviews on their products (the Mafia) as well as them paying teams to plant fake reviews on competitors products to have them tank in ranking.
The other one that was interesting was when an unknown Mafioso paid a team to click on competitors ads on Amazon. The net effect was that they consumed the daily budget by 6 AM and they went through the day without a single sale. In other words, the ROI went to zero on advertising.
Amazon denied it at first. He pressed on and provided details. After six months Amazon admitted they had determined this to be true. They refunded him some advertising money. They never restored the ranking he lost to the criminal.
Even worse, they absolutely refused to share any data with him (and presumably others). In other words, there was no way to seek legal remedies other than, potentially, filing a lawsuit against Amazon. Financial asymmetry aside, the biggest problem is that they keep very tight controls over the data. Which means you will have an almost impossible time proving anything unless you have the financial horsepower to hire an impressive team of attorneys to wage battle against an entire floor of Amazon attorneys. In other words, the little guy gets screwed, has to take it and shut up. Move on.