Do they have an asking price on the Testarossa? Or is it one of those cars where "if you have to ask - then you can't afford it".
I totally agree with DC33. Unless the car has been exercised on a regular basis and maintained properly, only covering 500 miles in almost 20 years of existance may be asking for trouble. It was also very common on Ferraris of that era to have the odometer disconnected.
If you do go look at the car again, take a few pics and post them up for us....?