@Anastasia43
Hi Anastasia, this is unfortunate for you that this has happened and diplomacy is probably your best course here.
If it were me I would have a talk with the guest and state that the payment had already been made by Airbnb for the duration of the original reservation. Try to discuss something that is mutually aggreeable, and then go to this guests reservation and click the 'Send or Request' money box and type into that box the amount you agree to refund. This way it will all be handled through ABB so there will be no confusion about who does what and, most imprtantly it will stop the guest trying to open a complaint through the Resolution Centre which could result in him having his entire amount refunded.
Any money which you agree on will be taken from your future hostings so, although you will be a bit out of pocket you still stand the chance of getting a reasonable review and keep your good record intact.
If you are having any issues with this Anastasia get onto the Sydney number 85203333 and explain your situation. They are pretty good and will help you to sort this out.
I hope you get a lot of great guests from here on, hey!
Cheers.....Rob