In dealing with my current round of deadbeat buyer 
issues I haven't left feedback for the (insert bad word of 
choice here), only reported him  but I do have the 45 
day mark circled on my calender so I can leave the 
feedback last possible moment. Argh I've been reduced 
to sniper feedback! 
But don't be blackmailed into forgiving!  You have a 
great reputation in this word of mouth community and I 
don't think feedback like that will hurt.  I always read 
both profiles when looking at Negs, these people will 
likely continue to buy and not pay and that will be 
evident.  
Plus I've seen the seller Drac is talking about, what a 
great way to deal with the problem!   
Good luck!