I'm not fully sure how it works, although I'm thinking the third party (HomeAway) also has a share of your funds. If true, then the homeowner can't refund what he never received. I like your approach of sharing the loss, and it seems you are now dealing directly with the homeowner. Perhaps your group and the homeowner could agree on a 'rebooking fee' of some amount (rather than a percentage). Wow, this is new territory for most everyone.