>>I've been sold based on "negative" reviews
Absolutely - I like Amazon's presentation of the top positive and top negative reviews, and the ability to view reviews by rating. I'll still buy a product with negative reviews, though sometimes I'll give it a pass if the negatives are credible and are directly related to my needs/wants.
Perhaps the big-time tort lawyers don't think Yelp has enough cash to bother with. Toyota has $20 billion socked away, and is drawing lawsuits like a magnet in a junkyard.