Sellers can report other sellers. Fraudulent Chinese sellers will post bad reviews on competitors’ stores and then report it to Amazon, so the competitor gets shut down. They will hi-jack listings, so the originator of the listing can’t edit them and has no control over them. They have bots search the products they manufacture, so when Marketplace sellers research products to sell the keywords are inflated for these products.

You can file claims with Amazon and report this stuff, but these same reporting mechanisms are used by dishonest sellers too.