However, you should find a good balance between good and bad comments, and you certainly should not find anything about them in the Better Business Bureau or similar organizations. You should also be wary if you start finding large numbers of lawsuits, especially class action suits. Another good place to look is in the promotional materials for the stockholders. This is the place where they explain to investors why they should be investing in their company. This often tells you exactly how the company makes money, and it can often produce some very eye opening results.
Press releases are also good places to find information, as are privacy notices.
Keep in mind that privacy notices can be changed, and there is some debate about their enforceability. These are statements of intent, not legally binding contracts. I know this sounds like a lot of work, and you may not want to do it all for every single little free service that you get. However, let's say you are using free web space from a provider. The point is simple - rarely is there ever a free lunch that is honestly and completely free.