You can sue the friend. The friend either (1) violated a verbal or oral contract (the agreement to pick up the tickets) and/or (2) committed fraud; either would give you grounds to sue him for the $646 plus also for other costs you have incurred as a direct result of the friend's action, like the any nonrefundable airline tickets that your husband no had no use for. You should be able to sue him in your local costs, and you also should be able to sue in small claims court, where you can represent yourselves and save on court and lawyer costs--though it will still cost you something in terms  of money and, of course, time. There is no way to get the money back but suing, though you might also be able to contract the police in the friend's town and say that he stole from you.