Some people I just don't understand

So, I was reading a review for a scifi book, and the reviewer was going on in some detail as to the 'poor writing' of the story. Or at least what they considered poor writing. They mentioned at one point how most of the book (I think they said 80 percent) was about sex, and all nothing but sex. Which if it had been, it probably would have been a best seller, but I ended up wondering if they were reading the same book I was? Yeah, I think there were a couple of sex scenes in the book (mild I'd say by today's standards) and sex was alluded to more than once (as in people were sleeping together! The horror!)

But I really don't have any idea where the hell they came up with that idea. To be honest I think that they didn't read the book at all, or if they did, they read some of the book, and then tossed it and wrote their review. But I've seen this before, and I often wonder if they even really bought the book, or if they did buy it, if they just returned it (so they never really paid for it, but still get the tag saying they did) so they could just write a nasty review that has very little relation to the story.

I used to always give the 5 star reviews a bit of a careful view, because you'd wonder if friends or family wrote them. But these days, I'm starting to wonder about the negative reviews, because I'm starting to see negative reviews on books that have very little relationship to the story. They'll take an aspect of the story, slag it, and then claim that's going on throughout the book. Maybe it's just the latest form of trolling?