I think you’ll get further with them by posting this story on social media. They might worry potential hosts would start looking into more things like this and decide not to use them. Other platforms don’t do things like this.
It will hit home for other home owners as this could happen to anyone. The guest could have gone to the grocery store and had you reimburse them for purchasing a new one as soon as they wanted right? Did the coffee maker break? Obviously this is a shady situation the guest must have asked Airbnb for money based on this that dialogue would be interesting to see wish we were a fly on the wall.