You could ask the guest to pay for the damages to the socket.. or get AirBnB involved if they refuse. You are insured with AirBnB for guest damages, but they don't cover 'wear and tear'. They do make it quite a palaver to claim.. However they normally will pay out if you're persistent, you have the evidence, receipts etc. You could also take a damage deposit?
Personally, I don't think it would be very easy for a guest to prove that your house damaged their car. However if you have an EV charging station, then you could cover your back by having a qualified electrician test it to confirm it's working properly.
I think that's the future - EV charging stations at properties. In 5-10 years, most guests will probably be using electric cars, so the idea of restricting guests charging will be unsustainable in the longterm. I would suggest eventually getting an EV charger which charges guests for the electric they use.