Yelp's reviews, however, are of dubious value. No review, reviewer or review website can ever be perfect, but Yelp could do a whole lot better. Most importantly, the reviews on Yelp tend to be overly positive. Remember, Yelp takes advertisements from the same businesses it reviews. No business would buy an ad of any kind on Yelp if their own review is negative. Because every business that is reviewed on Yelp is also a potential advertiser, it suits Yelp's on financial interest to keep as many reviews as possible positive.
Yelp does a number of different things to keep the reviews positive. Most obviously, Yelp allows a business owner to pay to have a preferred review at the top. And, at the top of each review is a purported "average" star rating. I did the math on Yelp's own reviews of itself, however, the average is just wrong. Guess which way!
Yelp also displays reviews -- and even deletes reviews -- in a manner that is far from transparent. Yelp will not release the algorithm it uses, but they do say popularity of the reviewer counts. Positive reviews are popular, so this pushes positive reviews to the top and keeps them listed. Yelp also fails to tell people when their reviews have been removed. I see no valid reason to remove a review simply because the reviewer is not popular. Let the consumer sort by popularity if he wants, but do not just take reviews down. And, when the reviewer logs in, he actually sees his own review, as if it is were published.
There have also been allegations that Yelp engages in practices that are little short of extortion, such as offering to move good reviews to the top for money, then doing just the opposite when the business owner refuses to pay. I have no personal knowledge of any such incidents, so I will simply provide a link to an article that contains more detailed allegations.
Finally, I recently had Yelp remove one of my reviews, with notice to me, for an alleged violation of their rules. I was looking for a painter, and found one on Yelp. He had one five star review. But, when I called him, it became clear that he had written his own review on Yelp; foolishly, he did not even bother to use a pseudonym. The name on his answering machine matched the review. So, I never spoke to the guy and never used him, but I did post a review on Yelp calling him out for cheating. Yelp pulled my review, saying I had no personal experience with the business. I think they should have thanked me!
All that being said, Yelp is still useful. You can find a business, its address, phone number and website in a flash. Even the reviews are of some value, just so long as you know what it is you are getting.