DR FJL, I wish I had a specific example of what I meant re Amazon. It's not a typical review of a typical item. Ever. It's when there are gushing reviews of something widely known to be egregiously bad or dishonest, or an equivalently bizarre attack on something good. It's something that stands out enough to raise the eyebrows of even a casual browser.
Oh, here's one. A few years back someone issued a Blu-ray of the Fleischer animated GULLIVER'S TRAVELS, hawking it as an important advance in restoration using techniques that successfully transformed it into: widescreen! All they had done was distort the picture by stretching it, and they actually issued it for sale that way. In other words, here was a completely dishonest product, with a few people gushing about what a revelation it was, and going to great lengths attempting to deflect all negative comment about it.
I think I've also seen people shilling for bootlegs and other such things. Wish I had examples. But that's all I'm talking about. Just plain (and fancy) dishonesty in reviewing.