In addition to the advice you've already been given, once you've added the bidder's User ID to your Blocked Bidders List go back to your Selling Preferences and tick the box next to the option that reads "Don't allow blocked buyers to contact me." If you do this then nobody on your Blocked Bidders List will be able to contact you. You don't need to keep on doing it every time you add somebody to your Blocked Bidders List - once you've activated the "Don't allow blocked buyers to contact me" function it remains on by default unless you change your mind and decide to deactivate it for some reason.
