Im not totally sure this falls under the same as Loshon Harah
1) Yelp reviews can be written by ANYONE Jews, Non Jews , even people who havent even gone into the place
2) Most real reviews (You can tell which ones are revenge vs which ones are constructive critism) can help the owner. Posting such things as the service took too long might help the owner speed up the service before customers walk out
3) Frankly JMO nobody is entitled to your business, if the food is lousy and the service stinks, other people do need to know about it and should have the same right to avoid