From the consumer side, Yelp has been useful because they have both negative and positive reviews.

I know Yelp is more critical, so if a business looks good on Yelp and the negative reviews seem like things I don't mind or that shouldn't result in such bad reviews, I am fairly confident I've found someone I want to do business with. (To give you another example of my thinking, when I read about a product on Amazon, I go to the 1* and 2* reviews, there are always some, and decide if they're substantive or if they're fluff, like the shipping took an extra day or the credit card was declined. So I look at negative reviews but I read them independently.)

This doesn't mean Yelp is fair. But it seems there's more information content on Yelp than on most other places, in other words some other review sites are close to useless.