Yes, I've seen articles where people who do this say there are a bunch of Facebook groups for exactly this purpose. Manufacturers/sellers ask people to buy their goods on the group and write good reviews. Once they get the proof of the purchase/review, they Paypal (or whatever) money to the "reviewer." I remember an article I read where some woman's house was overflowing with junk she didn't want because she was writing so many of these fake reviews. I would think Amazon could apply their awesome machine learning to figure out which accounts are pumping out these suspect reviews and perhaps de-prioritizing and maybe even rate limiting and delaying publishing of their reviews. I'd think that would do a lot to alleviate the problem.