You cant take a non refundable deposit due to distance selling regualtions surely?
I take £100 'reservation fee' which becomes a deposit once the customer confirms on site.
I think its only fair if someones travelling to give them first refusal.
I'd take the mans £100, call him when the car arrives, give him first refusal, if he doesn't buy, call the other 2 and offer the same.
Love having customers fighting over cars!! ha ha