Don't think private messages are enabled on this board. You can add users to your buddy list, but I don't see a way to PM, unless I'm missing something. Guess you just have to go to their store and use their contact link.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .