Maybe the best thing will be that he doesn't pay you and is so embarrassed that he is ashamed to contact you again. I've had a couple of situations like that over the years, and decided that never hearing from them any more was worth the value of the unpaid bill.
I've only ever had 2 people not pay me & I considered them gifts. I don't require payment to e-file as lots of clients mail me a check after pickup and that can take a full week.