I'd give the guy serious $hit about wasting my time, and the fact that once he bought it, it was HIS problem, and that he should have gotten a PPI.  
I'd flat out tell him not to waste anyone else's time - if he plans to buy another one, get it checked BEFORE he agrees to buy it. 
Aside from that, if it were me, I'd tell him tough ****************.  If I got that much money for my car, I'd tell him I'd go half on the RMS and strut, and THAT'S IT.  AND that he'd be LUCKY I was doing that.  CAVEAT EMPTOR!!
		
				__________________
				2001 Boxster - Grey on Grey
1969 911T Targa - 'Stinky'
http://www.zoto.com/frayadjacent/img...f27a-4a399.jpg   <---- my car.   ^ crap I post. 
"The existence of the flamethrower is evidence that someone, somewhere once said 'I want to set those people over there on fire, but I don't want to have to walk over there to do it.'"