Actually, Yelp can play game like this and be profitable.

If business have a good rating on Yelp, then that pretty much mean that business is ok. However, a bad rating might be because business was not nice with Yelp sales people.

That is ok because they target small, unestablished, businesses which you will never discover that they are actually excellent business because they have just one star review.

In other words, advertising at Yelp does not guarantee you a good review. However, not being nice with their sales people might get you a bad review if you are a small business.

And this is absolutely nothing new.