happened here a few times, we deal with batteries so acid spills occur occasionally and the company pay for any damage to cars etc, but from a purely legal stand point I have no idea how it should go tbh
I had nasty one as well a while back , stupidly left the turbo uncovered whilst there were some road works up the street, they must of been cutting iron works or something as the whole car was covered in swarf, and it had rained, so the swarf turned to rust and stuck to the paint. I was absolutely fuming but literally didn't have a leg to stand on, thankfully I tried a patch in an unnoticeable area (like the tins always say ;-) ) with the old clay bar and low and behold the chunks of stuck on rusty metal let go and came of virtually scratch free. car still needs a damn good PC though really as the paints 3 year old now and showing it.
its just so frustrating as others have mentioned that people only seem to see cars as tool and not something anyone can actually enjoy and love owning and care about