My SF agent knew collector cars but despite loosing business he also knew when you were better off looking somewhere else and would come right out and tell you. For anything that is in better shape then normal his advice was always to keep all receipts and records because it's up to you to prove why the car is worth more if they put a low value on it. For at least one car I also had an appraisal done so that I at least had documentation to support what condition the car is in if it was ever stolen or destroyed.
But if it's a vehicle that could be an issue it's far easier to deal with a company that specializes in it to begin with.