@Nick1752
Damage to the roof of a car is quite specific. Not something that would happen in the supermarket car-park. Not something that would happen if the goose ahead of you at a set of traffic lights rolled back and hit your car and then blamed you!
There are not too many situations where a car roof, in isolation, gets damaged.....unless it's the result of a suicide from an upper floor balcony which your car just happened to be parked under!
Get them to send you photos of the damaged car roof. If there is in fact damage it may be possible that the damage was caused by a previous encounter with a garage door, or a car-park boom exit gate, but Nick, that is unlikely. It is probable that the photos will be accurate!
Secondly, is it possible for your garage door, by gravity, to simply close itself regardless of whether there is a vehicle under it or not?
You know what sounds feasible with your property and what doesn't.......If there is a possibility that this door of yours did unexpectedly come down on your guests vehicle roof, then you are going to have to accept some responsibility for their damage. After all, the negligence is on your part, not the guests!
You can put in a claim to the Resolution Centre but, they will in all probability tell you to claim on your public liability policy and not offer you any further assistance!
Cheers........Rob