I was reading this article recently about fake reviews on Amazon.
I never worry about fake reviews. If you take your time researching each book before your purchase it, then you should be able to get a general idea of whether or not you'd like a book before you purchase it.
1. Read multiple reviews. Don't buy a book because you read one five star review.
I read both five star and one star reviews before I purchase a book (and some reviews inbetween.) I usually assume all reviews are biased if they only have positive or only have negative things to say. So I take those reviews with a grain of salt.
I also look at what the negative reviews are saying. Something that annoys another reader won't necessary annoy me. For instance, I passed on a book once because the negative review was that the author lectures the reader too much on religious issues. It's not something I want to think about when I'm trying to relax and read. But another negative review for another novel I read once said that there was too much gore and sex in a novel. I'm very comfortable with any level of gore and sex, so the negative review didn't bother me and I decided to purchase the book. And yet another negative review for another book told me once that there was horrendous spelling and grammar for the book. I looked at the sample and it looked fine. That person probably found a couple of mistakes in the novel and was a grammar nazi who felt the book was ruined by that. I couldn't care less about a couple of mistakes.
I weigh the negative reviews and how annoying those books sound versus how intriguing the premise for the book is.
If the book is a retelling of a fairytale, which is something that I love, then people have to say something extremely horrendous for me not to try it. But if it's a mystery novel, which is something I rarely read, it doesn't take much for me to pass on it.
2. Remember that reviews are subjective.
My Dad is a judge and I asked him once how he can tell the difference between people who are lying in court and people who are telling the truth. He told me that it wasn't his job to tell the difference. He assumes everyone is giving their truthful view on how they saw the events occurring. The reason their viewpoints sometimes contradict is because people remember things and view things differently than one another. It doesn't mean any of them are lying.
In fact, he tells me it's more suspicious when everyone's story is identical because they probably rehearsed their story ahead of time.
So just because someone reviewed a book you hated with a five star review raving about it doesn't mean they are lying. And just because a book has both one star and five star reviews doesn't mean either side is lying either.
You just need to piece together the information you are given from all viewpoints of the book and figure out which viewpoint you are most likely to agree with.
Fifty Shades of Grey is not a book I was able to enjoy. After reading a third of the book, I was forced to put it down and doubt I'll ever pick it up again, but I don't think the people who gave it five star reviews are lying. They just view things differently than I do.
3. Read a Sample before you buy it. It's so easy to do with Amazon.
Agents do it all the time. They're able to figure out whether they click with an author and their writing within reading the first chapter. I can usually tell whether or not I'll like a book that quickly as well.
It's even better than reading reviews because it allows you to experience the book personally and form your own opinion.
4. I also use sites like goodreads that tracks books I like and want to read and gives me suggestions of similar books that I might enjoy as well. I don't enjoy all their suggestions, but when I put them through the above process, I can usually tell whether or not I will enjoy a book.
Also, trust a friend with similar tastes in books to what you have and their thoughts on a book more than any review you read online.
Suggestions from others can help a lot as well.
Everything, like reviews, samples, and goodreads is just a tool to help you find books to read. None of them are foolproof and they aren't supposed to be. Use them right and they'll help you a lot.
Whether people write real reviews or fake reviews really shouldn't matter if you take the time to make sure you're being a smart consumer.