@Si6 Something similar has just happened to me. I had a guest check in in the afternoon and the next morning, woke up to a message saying she was checking out and wanted a full refund because there were ants. Now, there were ants, tiny ones that come in Spring but I never know if or when they're there unless someone tells me. So before I could even take care of them she said she was leaving. I said the apartment was still totally habitable it was unreasonable to get a full refund without giving me a chance to get rid of the ants. Anyway, we didn't see eye-to-eye, and I refunded her for the one night she had to stay there and we agreed not to review each other. I considered the issue resolved.
Next thing I know AirBnB has "canceled" the reservation, refunded her in full, and it's going to come out of my next payout! They never ever contacted me to hear my take on the disagreement, and have yet to respond to my calls. I hate this company. I understand the desire to placate guests, but with their profit margins they could refund her themselves if they think they need to keep her happy. Just like credit card companies do in disputes. The disregard for hosts is legendary. May I remind AirBnB that you get zero guests without hosts.
I also list a property on VRBO. They have their own problems, but I think I'll just go over there and see how it goes. Or do long-term rentals elsewhere. The only recourse in a situation like this is to take your property elsewhere.