I agree - in a lot of these Amazon discussions on HN a lot of people seem to believe Amazon does nothing. But if you look at e.g. seller forums at Amazon, ther

I agree - in a lot of these Amazon discussions on HN a lot of people seem to believe Amazon does nothing. But if you look at e.g. seller forums at Amazon, there are a lot of large threads about the opposite problem - Amazon taking out lots of reviews the sellers consider legitimate. So clearly they are doing something, and it might even be that only a small minority of fake reviews get through, but due to Amazon's scale there are still a lot of them.