Missed the edit window.
Also, even if Yelp themselves are not engaged in any nefarious practices, it’s still worth using a rather cautious eye when reading the reviews.
Business owners and employees can easily place positive reviews on the site themselves, and there’s also nothing to stop a competitor from posting a negative review in an attempt to sabotage someone.
More generally, while a small percentage of Yelp reviewers are serious reviewers who write about lots of businesses, in many other cases it’s clear that some people sign up specifically to write about one business where they had a bad experience. While there’s nothing unethical about this, even great businesses have some malcontent customers, and bad days where they fall below their usual standards, so it’s probably not fair to judge a business based on the complaints of (what appear to be) a few atypical cases.
I also tend, rightly or wrongly, to judge Yelp reviews based on how descriptive and reasonable they seem. If it’s a one-line review saying “This place is the suck!!! Don’t go there!!!” i usually just ignore it. But if the criticism is substantive, and appears to be based on specific reasons or problems, then i’m more likely to take it seriously. Similarly, if the review just says “This place is awesome!!!” i’ll move on to the next one, but if it’s a detailed review that praises specific things, then i’ll pay more attention.