I think it's similar to evaluating anything you want to buy. Read all the reviews. If 20% of the reviews say that the hotel is next to a bar and that there is late night noise, then it's probably next to a bar, and if you don't like late night noise, you want to be on the other end of the hotel. If 20% of the reviews on Amazon say that the product broke in less than a year, and the other 80% say that they're really happy, then you have a 20% chance of your product breaking in less than a year, and and otherwise you'll be happy. I don't think you should assume that the reviews are lies, just that some people are pickier than others, and some people had better luck than others.
Before we rented our current apartment, we looked at the reviews on the property management company. On average, they're quite bad. While our experience is a bit colored by these reviews, the truth is that most of the complaints I've seen carried out against our neighbors while our own experience has been better (though I'm not holding my breath at getting our safety deposit back--the biggest complaint was that the company rips people off on the way out). On the flip side, my neighbors and I have the same landlord, so if some review said "PM company was very responsive and totally awesome to work with, and my landlord is the best" I wouldn't say it was a lie, I'd suspect that their landlord has pushed the PM company to be responsive to their renters' needs whereas ours are trying to do things on the cheap.