I don't necessarily put that much credence in them, as it depends on the reviewer.  OTOH, if the reviewer is experienced and his other reviews run a reasonable spectrum, his may be the most important review you find.  On the other side of the coin, I came across a 5/5 review a couple days ago in the midst of a bunch of 8/9/10s, but when I read his review, he'd had a great time and had nothing bad to say.  He obviously has some sort of disconnect between his ears.

No, There is no reasons to search for bad reviews. Nobody wants a bad fuck when they are paying for it. That's like going online and paying to download bad porn. Sorry, but most of us want to find the girls that will give us the fuck of our life.