c bc.... please, in future never do a Mutual Cancellation. ALWAYS open / close a non payer dispute if the 'buyer' does not pay you

that way neither side can leave any f/b and if they leave you a neg before the case is closed ebay will remove it. 

regarding fb on this one?  DO NOT, ever, be tempted to leave a 'false' positive, i.e. positive dot with neg comments.  as sellers can ONLY leave a positive, just do not leave any fb in this instance.