In our post Guidelines for New Authors, we said:
Guideline #3: Don’t do giveaways on GR. That attracts trolls. Trolls like free things and they are usually the harshest and many times the most unfair critics. For example, take a look at this screenshot where a troll says: “It was free and I’ve heard bad things. I’m so excited!” This particular troll was trying to get her friends to do a buddy read so they could trash a book they got for free.
In a recent HuffPo article, Maddie Crum elaborates on the same subject: 
Some of the examples she gives are priceless. Literary masterpieces trashed by those who shouldn’t be reading them: 
This is why we counsel authors not to do giveaways on GR. GR is swarming with readers like this (not all of them are like this, but many are). In this case, we recommend listening to the words of the Apostle Matthew:
“Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you.” King James Bible, Matthew 7:6