Overall mechanically sound vehicles, gas or diesel. I would be particular about maintenence on the TDI. Where is had been serviced - was correct oil always used? Fuel filter changed at proper intervals etc. If its a TDI and you are expecting it to have the extended emissions warranty have the vehicle checked and make sure previous owner didn't void the warranty with an illegal modification or tune. Check for SWS during a road test, will need to get up to 65 or 75 mph cruise to check this. (Much written on here about SWS) Also watch for vibration and SWS under braking, a sure sign the rotors are warpped and need replacement $$ for new ones. On the inside make sure all controls work, moonroof if equipped, seat memory buttons, mirror controls, heated seats, steering wheel, etc if equipped. Lock/unlock each door with touch system to make sure all are working properly. Nothing control wise would be a real deal breaker, just realize if something doesn't work and the seller is vague ("ugh its probably a fuse") it really probably a module or relay and will be $500. Negotiate appropriately.