It’s always a good idea to be on the lookout for fraud, of any kind. Where there’s money to be had, there’s incentive to make your product look a lot better than it really is, or to try to cover up flaws.
When I look online for a product, I generally look for bad reviews, and read those carefully to see if the things that the reviewer are complaining about would affect me. It usually works out quite well, as it did when GoddessJ and I recently helped her mother pick out a new printer.
A primary advantage is that it avoids any kind of fake-review fraud. No one is going to post bad fake reviews for their products — they’re a lot harder to fake, because you have to be very specific about what you didn’t like, and it’s hard to come up with things that could be called bad, but that people wouldn’t care about, without sounding very artificial. And if you do get a nasty customer who posts bad reviews for no reason, it’s generally pretty easy to spot by comparing them with legitimate bad reviews.
Also, sometimes you’ll find the bad reviews on the manufacturer’s own site, along with their rebuttals, which can be very informative… I tend to trust a manufacturer that accepts public criticism, and defends against it in public, a lot more than one that deletes any post or article critical of their product. The former are as rare as hen’s teeth, and there are far too many of the latter.