Problems with non-payment are often easier to prevent than to cure. I have found that placing a notation on the work performed indicating the the work remains your property until the client pays for it and that use of your property is expressly conditioned upon timely payment  works quite well.

I had a problem a while back with a slow pay/no pay client. I told them that they had the choice of paying me or returning my property to me unused (with a written statement from them that it had not been used in the closing). Otherwise both they and their client could come to Connecticut to explain it to a judge. They had used the internet to communicate their work order, and it had been printed by a computer located in Connecticut (my computer). As such they had submitted themselves to the jurisdiction of the Connecticut courts under our Long Arm Statute. They were most eager to pay my bill.