I think what they do is weld nails to the outer door skin and pull out the dents, cut the nails off and then finish with bondo. At least that's how they fixed the door on my now deceased firebird. I'm really picky and I hate bondo because of how it cracked in the 70's. But I have to admit, I couldn't tell that the door had been repaired and since they blended the paint, I couldn't tell that the car was painted. Not bad for fixing a car with original paint that was 23 years old. And I was able to keep the original stickers on the inside of the door.