Also, with bad reviews, you can keep in mind if the bad reviews seem to be legitimate complaints, or whether they're just written by either someone with an axe to grind or someone who doesn't understand the purpose of the product. For example, some negative reviews of textbooks on Amazon seem to be people who are reviewing a course they took using the textbook. And some negative reviews of restaurants on Yelp seem to have wanted the restaurant to serve a different kind of food than they do.