Given how many times "Google is evil because it destroyed Yelp (not because Yelp is a trainwreck)" headlines cross the HN front page, arguably, no one trusts Yelp.
Hackers News titles are not a reflection of the society at large.
This isn't a counterpoint, but I absolutely don't trust it. I've heard too many stories about them removing bad reviews for businesses who buy ads.
I've only found yelp to be trust worthy in some cities, not universally.
I've found yelp to be completely untrustworthy, in every city, everywhere. What people think in the aggregate and what some individuals think are very different things.