Take the car to your insurance company and have them determine and give you a statement in writing if they think the car has either been hit or has hit something. In the case of the car hitting something it would be an insurnace claim and these people are experts at determining what is damage by hitting somthing
The dealer is most likey full of shit and trying to make money off you.
Are you sure that you never left your car with anyone? Like valet parking or an oil change place or something where you had to leave the keys and come back? It only takes a few seconds to screw a car up. It is why I never leave my keys with anyone.
