[Don Plumley]

The purpose of business is to create profitable customers. Customers that are not profitable, given appropriate opportunity to become profitable, should be promptly fired.

Invite "Jim" to come and pick up his car. "Jim, there appears to be an alarm system in the car that was not here before I painted it. Might that have been the problem? Perhaps you should have taken it back to the alarm installer to correct your radio problem instead of me." If he has one of those head slapping moments, present him with the final invoice which includes the time and materials for the radio install.

If he does not come clean, after he pays, you can suggest that for future body work he take his business elsewhere.