I have been having this discussion elsewhere as well, but this seems especially obvious in Amazon: all ebooks are apparently brilliant, and self-published especially, even if from cover and sample chapter it seems they are complete tripe.
I looked at all Kindle books, and this is how they are broken up by rating (today):
Avg. Customer Review
4 Stars & Up& Up (698,767)
3 Stars & Up& Up (801,494)
2 Stars & Up& Up (828,052)
1 Star & Up& Up (851,164)
So, out of all books that have been rated at all, only 152397 (less than 20%) are rated below 4*. How is this helpful to any reader? Everything is super-duper good, how is one meant to make a selection based on that?