Another factor that reinforces your conclusion (you can't prove who did or didn't buy them) is that a smart botmaster would have their fake reviewers also revie

Another factor that reinforces your conclusion (you can't prove who did or didn't buy them) is that a smart botmaster would have their fake reviewers also review random businesses that did not pay them. It makes it harder to detect that they're fake. For the same reason bots will try to friend random people on Facebook, follow random accounts on Instagram, etc...