Don't respond to the messages.
Go to the policies link at the foot of the screen and 'S' for spam. There is a contact link in there.
Is the member's id on your blocked bidder list now? If so, go to your buyer preferences (you don't have to be a seller to do this) and tick to block messages from people who are on your blocked bidder list. It won't kick in immediately if you have been in a recent transaction but it will prevent future problems.
