If the car has the computer command ride option, make sure it'* working OK or better yet, replaced with the air shock replacement. Examine the tires for evidence of worn struts. The CCR is expensive to replace. Check under the carpets front and rear for water leakage, especially the corners of the trunk and under the spare. If it has HUD, make sure the windshield has a logo that says "for head up display" and/or make sure you don't have a double image with the HUD ( indicates regular glass was used.to replace original.) HUD windshilds ain't cheap. Listen to engine carefully after it is fully warmed up for any tell-tale knocking noises. Make sure the */c is working OK on a test drive. You should be able to drive normally (easily) without going past 0 boost. When you do put your foot in it, you should see the boost build and feel a marked difference in acceleration. Let the car idle when you return from the test drive and while you look it over. Check the oil pressure, should be 35 or 40psi at least when idling hot. Check for overheating. Look under the car for any drips. Check the coolant recovery tank for an oily scum line indicating gasket failure or worse. A super clean engine makes it hard to tell if there are problems. Smell the nose of the supercharger by the pully - if it stinks, the oil has not been changed recently. Check the trans fluid - should be light red and clear and smell like trans fluid, not brown and burned. Examine the car in daylight. Sight down the sides for evidence of collision damage or body work. Look under the car for rust, oil, damage, things broken and hanging down. Look at the insides of the tires for evidence of leaking brake fluid. Try everything on the car. Have fun. Take your time. If the owner doesn't want you to look closely, walk away.
 check the bottom inside edge of the doors for rust.