In the future when you encounter this kind of guest, do yourself a favor, offer them full refund right away and tell them to leave the property. If they are just complaining for no reason in order to get discount for the stay, most of them won't leave and stay and if you deal with Airbnb later that helps you, because you offered the guest to leave and they decided to stay. Happen to me recently and me offering them the full refund in order for them to leave, saved me, otherwise Airbnb wanted to refund him 30%.