I bought this little gizzmo the other day - superb little paint depth gauge for £50 and should add, am in no way connected to the retailers.
Factory machine paint finishes are around 120 microns and thinner than aftermarket paint work which is normally thicker around 200+ but you get an idea from measuring other panels on the car.
Inside the doors are always thinner from the factory so anything as thick or thicker than outer panels points towards major damage.
You get the idea..
Every car is different, some panel towards the front will have more paint than the rear etc, so best to cross cross check ie n/s wing thickness to o/s etc.
Works a treat, just tested it on two cars with known accident damage!IMG_9818-1 (dragged).jpg