This episode of reply all show how hard it is to identify fake reviews and what seller are doing to fake it. Really interesting in my opinion.
https://www.gimletmedia.com/reply-all/124#episode-player
Gaming the rankings/listings isn't an issue exclusive to amazon, every single website has this issue, in fact even phone books (remember those) had to contend with people listing their name with leading A's to try to get to the front. Gaming listings is as old as lists and until we can come up with a solution to that problem we're always gonna have problems like this.