One of the great things about the internet is that it allows people to post reviews of products and services that they have used. For hotels this is especially important since you will probably have to book your hotel without actually having seen it. While the reviews can be helpful they are of course only of any value if you can trust them. The question is just how trustworthy are online reviews of hotels.
Obviously how trustworthy the online reviews of hotels are will depend in large part on where you are reading the reviews. Clearly you are going to want to a site that is not in any way affiliated with the hotel that you are considering. You are also going to want to stick to one of the larger review sites since these are going to be much more difficult to manipulate than a smaller site would be. In fact it is entirely possible to create a site that is nothing but fake reviews if you want to. This is why want to stick to one of the larger better known sites.
The other big thing that you have to keep in mind when you are looking at hotel review sites is that you can't rely on just one or two reviews. Anybody can put a review up on the site so if there are just a couple of them up there you really have no way of knowing who put them there or why. It could be that they were put there by somebody who is affiliated with the hotel, or they could have been put there by somebody who has an axe to grind, it could even be a competing hotel that put up a negative review.
Since you really can't rely on just a small number of reviews you are going to want to find a place that has a large number of reviews on them, the more the better. Instead of looking at what each specific review says you are going to want to focus on the general tone of the reviews. If they are generally positive then you can be fairly comfortable booking at that hotel, the opposite is obviously true if the reviews are generally negative.
One thing that you do have to watch for are the professional reviews, these are the full length articles that review the hotel. These can be a great way to learn about the hotel that you are interested in but you have to make sure that they are on a site that is trustworthy. There are some sites that will accept articles that are written by anybody, this of course means that the hotel owner could be the one who wrote the review. Again the best rule here is to make sure that you are reading several reviews.