Re: car accident -- claiming diminished value
I would say your first point of call would be to talk to your own insurance. They will probably suggest that you have an appraisal done. If that lists any changes to original, or damage evident, and you can prove that this was a direct result of the accident, then you can chase the dealer for the diminished value for that.
Just how evident is the change?
Getting new paint to match the original _exactly_ is notoriously difficult. The colour is easy enough, getting a resprayed panel or door to match the original lustre and surface quality is almost impossible. An expert will spot and document this type of problem.
Putting an exact number to the diminished value will be very difficult, but stick with it.
See if you can find an AGB (Allgemeine Geschäftsbedingung) from the dealer, and read it closely. Inform the dealer of your concerns, in writing (otherwise they have a legal out).
Most garages don't use their insurance when somthing like this happens, they must have the insurance, but only actually use it if the car is a writeoff (otherwise the premiums go up more than if they pay the repairs themselves).
If your car is proper top end of the market ask the appraisor if there are any lawyers specializing in classic car insurance, if yes, consult with one, but don't mention him to the dealer until it becomes clear that they aren't going to rectify the situation without you bringing out the big hammers.
In short, it depends on the car and on the damage.
A '53 250 Europa with one shiny door is a completely different story from a 400 with a new chrome bit without patina.