Yelp makes 96% of its revenue on advertising.
They probably make more money if reviews for a restaurant are in question. If someone spends 20 minutes clicking around on a list of restaurants to read the reviews and see if some seems genuine or fake... yelp makes lots of money.
If yelp reviews were 100% trusted, everyone would just click once, and then go to the highest rated restaurant.
Think that's the root of the issue. A review system should not be in the business of advertisement or any kind which could change the review ranks
The problem is there's no accountability.
Sure, we can sue them, but for what damages? How do you account for the value of lost business opportunities caused by Yelp selling your honestly earned ranking spot on their website to your competitor?
The only way to prove they've done something wrong is to commit corporate espionage and get the proof yourself, which would then most likely invalidate the ability to use that evidence for revenge.