The funny thing is, I bet a graph of their profits would be totally different. Companies like Yelp and Foursquare are actually in the blackmail business. They needed the users to achieve a massive amount of reviews. Now they just collect "protection money" from business to remove / prevent bad reviews and laugh all the way to the bank. At least, that is the only way I can see their move making any kind of sense.
I've never seen a place with an undeserved good/bad reputation. And I've seen a lot of reviews from those sites (and went to those places)
As the number of reviews increase the "I'll never go back to this place" begins to show, but they're compensated by good reviews.
Now, systematic bad reviews usually mean there is an issue with the place.
"Sponsoring your listing" helps if you have a small amount of reviews (something like 5 to 10 reviews)