There are some unpleasant comments circulating the net at the moment disguised as book reviews, particularly on Amazon and Goodreads where some readers almost seem to be getting their kicks from ganging up on authors.
I’ve just found the perfect response in this quote from Jules Renard:
Literature is an occupation in which you have to keep proving your talent to people who have none.
Feel free to use it if you get a particularly nasty (and unmerited) review on one of your books. I think I just might, too!