Amazon allows users to rate the helpfulness of individual reviews. They also note whether the reviewer is a verified buyer of that item or not. And I STILL find reviews on a popular item to be more overwhelming than useful.
Additional issues above and beyond outright lying include the fact that a lot of people who get a defective product leave a bad review instead of returning it. It's like they assume the defect is supposed to be a feature rather than a bug, and review it on that basis. That's not helpful. (And I'm not talking about items where dozens of reviewers got defective products - that's helpful to know, but the best of products are still going to have a dud or two go off the assembly line.)