EBay does very little policing of its own site -- that's what the "Report" link is for at the bottom of every listing. E-mails will go unanswered (except for possibly a canned response that doesn't help).
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 .