Once upon a time you could protect a book from drunk troll reviews by pricing it at a level where it would make them reluctant to spend the money.
Sad to say that doesn't work anymore. Drunk Trolls (trademark pending by now) will either buy the book and return it in order to have a verified purchase at Amazon (writers are not as dumb as some Drunk Trolls think, I know who you are and I saw what you did) and then return it. No financial outlay and they can savage your work at will.
The other choice is to not go through the hassle of actually reading the book at all, just go straight to savaging it. The routine seems to be to simply go through the list of everything a writer has written and trash all of them with the same short sentence. Clipboard is their friend.
What I want to know is what kind of parenting produced children/adults who behave in this way. I'm not taking personal responsibility away from them but obviously they do not know right from wrong, they have not assimilated the Golden Rule "Do unto others as you would have them do unto you" or even something new agey like "Random Acts of Kindness." Something in these people is so broken, that striking out anonymously on the internet is one of the few acts that can bring them temporary comfort from their psychological suffering.
But you do have to wonder. What are they doing when they're not on the internet? Are they in Fight Clubs? Are they playing the Knock Down Game (hit an old person on the street hard enough to make them fall)? Are they torturing animals? How broken are these people?