So I started to ponder over the "who's insurance should cover this" argument over this and then had a thought. Anytime I have made a comprehensive claim on my car, one of the first questions they ask is if someone else caused the damage. In my case it was either a broken windshield due to a flying pebble or unknown a hole backed into my car at a place with no surveillance, or someone stole my stereo. I'd assume that if I told them that my car burned down while at a shop while they were working on it, they would investigate and go after that shop for damages if the shop was found at fault. When I worked at Sears Auto Center, we paid for any damages incurred to a car while we were working on it. I don't see how a smaller business would be able to be immune to this scenario and just tell the customer to go through their insurance. I would have personally gotten insurance involved immediately. Keeping them out of the equation is a bad idea no matter how good of friends you think you are with the person / buisness that caused the damage. It's a shame you didn't have collision / comp on your car, because you could have started the claim with them, and let them handle the rest.