Really -- your best bet for dealing with product reviews is doing a little bit of filtering of your own on them. How many reviews does a product have, total? If we're talking only "dozens", then several 5 star fake reviews can really push the product's ranking up unnaturally high. If we're talking thousands? Then that's a good sample size to be confident the number of stars for the product is fairly accurate.
It's also about reading the text of the reviews. Does it sound like a legitimate review by someone who really used the product? A lot of the fake reviews I've seen tend to be short, with generic comments about it being the "best one they ever used"... that sort of thing. Others are blatant copy/pastes from reviews written before by somebody else, for a different item. So doesn't hurt to highlight a chunk of a suspect review, and Google that string of text. See if it matches other reviews.
I can't say I really went wrong with almost anything I bought from Amazon, but I was already looking for a specific, known quality brand of an item, or stuck to items that have been sold for a little while and had large numbers of overall good reviews.