Depends on the negative review. You ignore all the "it sucks" reviews. But the ones that go into detail about why it sucks are usually accurate. At least in my experience.

And in terms of trying to game out the fake reviews, I've found relying on the 2 to 3 star reviews are the best. The liars who are trying to trash the product tend towards 1 star. The liars who are trying to sell the product almost always go for 5 stars. 2 to 3 stars, sometimes 4, are usually the people who actually bought it.