Just to be clear: Blocking prevents that user account from seeing your posts while they're logged in. They can see your posts when they log out. They can create a new account. But either way, they can't comment on your posts. You can't see their posts either, while you're logged in. When you comment on other people's posts, they won't see your comment. And they won't be able to plus-mention you.
On Google+, blocking someone makes that account vanish for you, and makes your posts and comments vanish for them. It's a very complete termination of interaction between you and the troll.
It's one thing to know how to block. It's another to know why. I've noticed reluctance by many users to block. It feels like an impolite and aggressive act. My view is that you should block every user you encounter who you believe disrupts conversation, exhibits abhorrent values or who offends you in any way. There are two reasons for this approach.
First, if you're offended, there are probably dozens, hundreds or thousands of other users who are offended, too. By blocking one person you benefit a great many more. Second, the troll you're blocking has the whole social network, in fact the whole universe of social networks, message boards and more to roam. Your account on Google+ belongs to you. Blocking who you don't like and circling who you do is how you end up with an amazing group of people to interact with.
Sometimes people will troll you not in comments on your own posts, but in someone else's. In that case, it's a good idea to send a private message to the poster and ask that they delete the comments and/or block the troll. Just say why. If the poster values your engagement more than the troll's, and they probably will, they'll block them for you.
Sometimes it's better to just not "feed the trolls." Blocking signals trolls that they "got to you," and that they forced you to take some action. Google+ offers two passive-aggressive actions you can take that are similar to blocking trolls, but the troll doesn't know he or she has been removed from the conversations.
The first is muting. When you mute someone, they're essentially blocked from your perspective -- you can't see their activity -- but they don't know it. They continue as if nothing had happened. Muting on Google+ is like blocking on Twitter -- it simply covers your eyes to their activity, which is otherwise unchanged. Muting is just like blocking, except you choose the Mute option instead of the Block option.
The second is flagging. If you believe a troll will go away if he or she gets no reaction (the theoretical foundation of the "don't feed the trolls" strategy), you can guarantee no reaction by flagging their comments on your posts.
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