TripAdvisor has been in the news lately because a fake restaurant had been rated highly by the site. A group of web users had created this fake restaurant in order to prove that TripAdvisor is not foolproof and can be gamed.
Of course, any website that allows anyone to submit reviews and rate the venue will suffer from this problem. It is just obvious. There is no way to fix this problem other than to allow only professionals to rate and review, but if TripAdvisor opted for that policy, the site would be no different to newspapers that publish reviews by travel editors. It is the democratic nature of TripAdvisor that makes its database so vast.
When looking for a hotel, it is important to determine the price. The best way to get the price is to go to the hotel website itself. After this, I tend to look at the quality of the place. TripAdvisor reviews are filled with angry people who vote a hotel down over minor problems. I do to some extent rely on TripAdvisor rating because ratings that are too extreme on the downside should be cancelled out by rating that are too extreme on the upside. Other than that, I rely on TripAdvisor's photos to judge the quality of bathrooms, beds, and so forth. Pictures don't lie. I also make sure I use other websites, e.g. Google Maps, or I do a Google search of the hotel to see what newspapers and blogs say about it.