Not the OP, but this reminds me of a similar experience I had with a book called Space Opera a few months ago. Don't remember where I first heard of it, but it was being touted as comparable to the Hitchhiker's Guide. All the reviews on Amazon were 5 stars, and since the kindle version was only $5, I bought it without checking further. It turned out to be a pretty disappointing read, and nowhere near the caliber of anything in the Hitchhiker's series. I remember while reading it wondering how could all the reviews have been so good. I just checked fakespot, and it had an F rating with 92% low quality reviews as of April 25 [0]. I then had fakespot update the analysis, and it's now a D, with 41% low quality reviews [1]. So it seems like the fake reviews were bought to get things jump started, and now real reviews are catching up. Now that I think about it, it's probably a fairly common way for authors and/or their publishers/publicists to get the early sales and hype going.
There are groups where ebook authors get together to essentially cross-review books of other members.
I remember reading an exposé recently, which I suspect was posted here, but I can no longer find it. (An other dropped out of the group(s) due to ethical concerns.)
Self published ebooks also fall under the category where a high proportion of the reviews are likely to be useless for evaluating the quality of the book even when they're noncommercial and sincere, because the initial reviews all come from close friends and family who are impressed by how creative Jonny is or hardcore sub-subgenre enthusiasts, and unless the book sells really well or is utterly atrocious rather than merely a bit mediocre there will be comparatively few reviewers interested in contradicting them.
Hmmm...can't edit, but: I just looked at this again, and it's interesting to note that the Kindle version has an A rating and the print version has an F rating, even though they appear to share the same set of reviews.
