Okay, so this may seem personal...and it is, and it isn't.
I don't write a review for everything I read unless I loved it that much or I'm reviewing for an author specifically, but if I read something and feel it was deemed three stars or lower I write why.
What I did like about the book, what I didn't and why...this not only helps other readers find books (yes bad reviews help, but only IF you actually review)suited to them but it helps the author know what they need to work on...
So please, if your read and feel it deserves three stars or less, please write a review use the sandwich effect...one good thing the bad and end it on a good note. This helps authors.