Use common sense when looking it over, I'd ask to look at all the receipts to prove its got a new head and timing belt. Make sure it's not leaking any oil or other lubricant's, look for smoke when you start it up if its smoking chances are its an oil burner. Also make sure all the fluids are at the proper level. Don't be afraid to ask the owner questions either. Obviously when your driving it put the car through it's paces check the clutch, brakes, steering and alignment. Make sure there aren't any unusual sounds, ticks or clicks.