This has happened to me in 2016. About a week after a guest left, I got a letter in the mail demanding thousands of euros because my IP address was associated with an illegal upload of an episode of "Modern Family." It identified the date and time, so it was clear which guest was the person responsible. I had to pay a lawyer to deal with the suit, and when I contacted the guest she acknowledged her mistake (forgetting to turn off BitTorrent while using my WiFi) and agreed to pay my lawyer's fee of around $100.
But I also contacted Airbnb's customer support to ask what they would do if the guest didn't agree to pay. I will copy in the response the Trust & Safety team sent:
" I have consulted with my management team about this situation, and unfortunately, if your guest does not agree to pay the legal fees you are requesting, Airbnb will not mediate in this matter. As a third party, we cannot charge your guest's security deposit for non-physical damages.
I want you to know that we do understand your frustration and we're sorry for this unfortunate event. As previously mentioned, we're incredibly limited with how we're able to help when it comes to these fines. You're of course welcome to request payment from your guest, but please know that this will not involve our mediation.
As per our Terms of Service, we are excluded from liability with respect to loss of data or any related fines or fees, or incidental, special, or exemplary, or consequential losses of this nature."
@David-And-Cheri1