Can I Block an unwanted Buyer?

I have a buyer who ordered two gigs then refused to pay for rest of the gigs their project required to complete. They left negative feedback but have now agreed to remove it if I give them a mutual cancellation.

Since this Buyer has proven they either can't or don't care to read instructions is there a way to Block them from placing future orders with me? I just don't need their hassles or them do additional damage to my cancellation rating.