In France, an agency created a fake company selling kebap sandwich on Mars. They had 105.000 views on their video, 46k followers, 20k facebook fans...and orders. What's scary isn't the fact people buy fake reviews/followers/etc. but the fact people actually believe in these vanity metrics and want to order afterwards.
People who are seriously doing this aren't paying $5 a review. They are paying $100-$500. At this point I just assume almost all reviews are fake. Especially on Amazon and to a slightly lesser extent Yelp.