Remove the spare tire and jack next time he's in...you can always eBay it and get SOME money off the deal...and he's in a bind when/if he needs it...IT AIN'T THERE!!!
Who's he going to blame? He didn't have the cash to pay you for a job well done...so you do a job on him and you get some of the cash...how much do you think it's going to run him to get the same style wheel/tire combo...let alone the jack, too?
Better yet, let him detail his own cars...and make a display in your business that makes an example of him as to why you don't extend credit to cretins...'cause "...this dumb@55 didn't pay...you all have to have COD or there's no return of the vehicle..."
Better yet...
Doesn't your state have "Mechanic Liens Laws" on their books? The customer pays in full or the mechanic has all rights to said vehicle 'til the full amount due is paid in full? Maybe you might have the right to file a lien against his vehicle...he can't sell it or the new owner can't title it 'til the lien is cleared and you don't have to chase his ass all over the place...