:-D AFAIK, It needs some ultrasonic handheld probe to determine a paint thickness. Anyways, dont worry about that. I doubt if even the dealer knows how to get it and check the same. They are used by specialists and in car factories I guess. Just check the PDI checklist and go through the whole list carefully checking out each and every aspect. Get hold of some expert mechanic to accompany you if you have lost faith just to make sure they are not selling you a bad apple. I doubt that they would go to such lengths though.