Its a fairly well known accusation that has many pieces of circumstantial evidence as well as many lawsuits.
Many business owners have claimed yelp salespeople have called them and tried to sell them the ability to bring down unfavorable reviews or that they would highlight them.
> “[T]he business owners did not allege sufficient facts to support their claim that Yelp authored negative user reviews of their businesses.”
The ruling was that if yelp manipulated ratings, that's fine, but there's no evidence they did. I don't know whether to believe they've done it or not. There's a lot of business owners over the years who report having gotten shady calls, but it'd be really hard to prove those calls are from yelp and not from fly-by-night scammers. I get calls from "Cardholder Services" and "Microsoft" pretty regularly, so it shouldn't be surprising if there are extortive yelp scammers.
Many business owners have claimed yelp salespeople have called them and tried to sell them the ability to bring down unfavorable reviews or that they would highlight them.
One google search away: yelp wins lawsuit that says they are perfectly within their rights to manipulate their ratings: http://www.dailydot.com/opinion/yelp-extortion-lawsuit/
"Yelp is pay-for-play, and the court says that’s just fine."