I too have had Realtors help me get my money out of these deadbeats. Its sure worth the try.
I'm curious if the buyer gave a reason for stopping the payment on the card. Was he dissatisified with the inspection, was something missed, or was his fee not what he thought it was going to be, was there an add-on charge he wasn't in agreement with?
If not, I would go after him fully loaded.
