Find the biggest scariest looking Black guy you can find and tell him to come with you and you'll pay him $50 bucks just to hand him a picture and walk away, nothing illegal....
Bring a polaroid camera and head over to this persons house whom owes you money... Knock on the door and step back a few feet.. When she or he opens the door take a quick picture of him or her, then immediately call over big old mean looking Tyrone and hand him the picture.. Tell him to walk back to the car and wait..
The client will be shocked, don't answer any questions, you then tell her or him they need to pay up immediately and then you walk away.. Guarantee you get paid on the spot or very shortly after..
You haven't broken the law or threatened that person in anyway.. You just took a picture and handed it to the mean looking black man.. That's not against the law...
That will send a clear message.. I've had to do that once many years ago and I got paid in full on the spot....