Bullying/trolling is a constant factor online, and it's surprising how tolerant moderators are of this behaviour. If you're an author, bullies/trolls will club together and systematically run down your books with vicious one star campaigns. It's not a big deal if you're well known but it can be horrible if you're new.
If you're venturing into writing, and you're wondering how to avoid the monsters online, here are some tips to help you spot them:
1. Bullies/trolls always cite "the rules". They tell you how authors are supposed to act, how reviewers are supposed to review, how you should promote a book, etc etc. Anyone who disagrees is subjected to a tirade of abuse. Fact is, there are no universal rules.
2. Bullies/trolls don't debate, nor do they stick to the point. Their point is to cause trouble, so they never give a straight answer to a straight question. If there's a good discussion going on, they'll interrupt by going off-topic, hoping to stir things up.
3. Bullies/trolls hide their identity. On Goodreads they are the ones with private profiles, on Facebook they never show personal pics, and on Amazon they have nicknames and don't list blogs, web sites etc. These people are cowards so they don't dare show who they really are.
What can you do about bullies/trolls? Ignore them. They want attention, they live for attention, so when they post, ignore whatever they say and respond to someone who is genuine. Then sit back and have a good laugh as you watch your troll go ballistic from lack of attention.
For an excellent long post on troll spotting, check out this Amazon post and this lovely Wikipedia article. If you're thinking of starting a group check out these (mostly serious) suggestions from Cracked.com.