How do you estimate damages for an Aircover claim?

Hello,

Our last guest left the roof windows open upon departure, despite clear instructions in both our house rules and the printed guide we provide at check-in. A storm hit just a few hours after she left, and when we returned later that night, we found significant brown water stains on several walls.

We first tried to resolve the issue amicably. She admitted to reading the rules and not closing the windows, but claims she’s not responsible because “the place was like that when she arrived” (we had indeed opened the windows shortly before her arrival to cool the space down) and she's "not responsible for the rain".

From our point of view, this is clearly negligence: she knowingly disregarded a rule, which directly led to the damage.

Airbnb support, contacted by phone, seems to agree with us in principle. However, the guest says Airbnb told her this type of damage isn’t covered and is trying to intimidate us into dropping the issue.

Our question: to file an Aircover claim, we need to provide an estimate of the damages. We’d like to first try cleaning the walls ourselves without hiring a professional.

• How can we justify a claim amount in this case?
• Is a quote required? An invoice? Can we submit a self-estimate if we handle the repairs ourselves?

Thanks in advance for your advice !