I get so aggravated when I read reviews of books when less than 3 stars are given. Some of the books I absolutely love, receive terrible comments on amazon! It is hurtful to the writer, but also the sales of the book.
Here are a few things that I consider when writing my reviews:
1) If the book wasn't good, I already wasted time reading it, why waste time writing a bad review? If the book was okay, and I had some constructive criticism, I would make sure to include that in the review.
2) When reading, I don't care if there is a missed comma or something like that. I am reading to escape my world, and to join the world provided for me in the book. It's about the story people, and what/how it makes you feel!
3) Regardless of what I think of the book, others will think differently. The authors are trying to make a living with their books. I would feel terrible if I personally didn't like a book; but someone else would have loved it, and they didn't buy it because of my bad review.
Therefore, I never post bad reviews! I would rather spend my time reading a good book :) How about you?