TLDR: Put a clear penalty in your rules/house manual, and Airbnb stands a better chance of backing you up.
I recently collected $250 from people who smoked in my cottage. When they arrived, I noticed that they reeked of tobacco smoke and made sure to emphasize the smoking policy, pointing out where ashtrays were on the porch and in the courtyard. Of course “NO SMOKING” is one of the rules they agree to, but there is also specific language in my house manual (online on Airbnb listing) and in my house info binder:
“SMOKING: I can’t emphasize this enough: there is absolutely no smoking of any kind (even vaping) allowed in the cottage. If you break this rule, we will know, and we will have to charge you $250 out of the security deposit. We really don’t want to do that. There are ashtrays in the courtyard. Please dispose of cigarette butts and ashes in the outdoor trash bin.”
We share a courtyard with these guests, and they were out there a lot, smoking pack after pack. So I kind of knew what to expect, although I had hoped they’d honor my rules. Sure enough, the smell was bad, and they had obviously smoked inside. I didn’t find cigarette butts inside (they did take out their trash as directed) but there was some ash in and near the (gas) fireplace. It didn’t show up very well in photos, though.
I called Airbnb and was lucky to get the CS person I did. She accepted my claim immediately mentioning I had been very clear in my manual/rules/online info.
The guest did end up paying, after sending me a nasty message. Oh, well.
I was really lucky – I had 2 days before the next guests to air the place out and wash everything I possibly could. If I had had guests arriving that day, it would have been a much bigger problem.