I have yet to find a review site that I trust implicitly. Issues occur because:

1. Some people are dumb. They will rate a business badly for something that is clearly not the places fault. For example I was with a family member at a restaurant, and they chose an item on the menu that had an asterisk by it, and the asterisk said "spicy". I know this individual, they think PACE mild salsa is incredibly hot. I warned them, and when it came, they were unhappy because the food was too hot for them. I've also seen positive reviews where the person attributes good outcomes, to nothing the business did.

2. Some businesses game the reviews to look good. They have servers, family, friends, and will even make up accounts to post good reviews.

3. Some customers have an issue, and decide to make it their life work to exact revenge on a business. This is the corollary to #2.

4. People don't necessarily have the same expectations. For example, my father could never give any restaurant that had an average check price of over $100 not including drinks for a table of two, a good rating. He just doesn't think it is ever justified. On the other hand, I have seen him complain about the food at a restaurant, and then remark later to someone that we had a "good meal there", and his justification is that "...it was inexpensive, so I expect some issues".

Until review sites offer some way to rate the reviewers, I'm afraid that sifting through the online chaff is pretty difficult.