Hello fellow Airhosts, I am in a quandry this very moment. Our guests stay in an apartment attached to our main house but with separate entrance and deck, however our venitlation system (HVAC) is shared in the upstairs so…we can smell odors coming from the apartment and vise versa. We have a strict no-smoking policy and I have some sensitivities to ANY kind of smoke. Meaning I can detect the slightest odors and this not is ordinary tobacco smoke. Very strong weed smell. I asked them to refrain from any kind of smoking indoors lastnight and stated we share a ventilation system (huhlo!) and she still denied they were smoking but into the night the odor waned (I have a sturdy airfliter) They are right back at it at noon today! They live in town so throwing them out feels a little like a security risk–not worried about a bad review just future retaliations. If I make another request to refrain, can I add that I will be keeping their damage deposit if they don’t comply? I will have to really do a thorough cleaning to get the smell out now. Is that within my rights to keep an “over and above” fee?
Not trying to be a prude, this just affects my own breathing and my own labor after they leave. Thanks for any input.
Have you told them again?
Are you absolutely positive it’s not a skunk in the neighborhood? This may sound stupid and I am not unfamiliar with weed however, I thought for sure that my guests were smoking in the apartment and then found out it was a skunk smell outside that was coming in through the AC 
My guests thought it was hilarious too, fortunately.
Airbnb does not charge a deposit. You have to prove damages and then the guest has to agree to have their deposit charged. Proving smoking is not easy. I would put your messages via Airbnb so there is a record. Also, if you don’t care about the review, you might want to state that you will need to contact Airbnb to cancel the reservation and ask them to leave if they continue to smoke. If this happens, Airbnb may refund the guest the entire amount. FYI - if it’s weed, you won’t have to do a thorough cleaning. The smell will disappear pretty quickly.
I agree with @Lynick4442. It will be difficult to collect a deposit for the smell, because AirBnB requires proof of damage through pictures. You would have to submit receipts for the damage, so the most you would probably get is get money for the extra cleaning supplies. I completely understand your frustration, as I have the same strict no smoking rules (and I even state no smokers allowed as I get sick even with the smell of smoke that lingers on their clothes and gets transferred to the bedding). If you have no smoking in your rules and they are still doing it, you can have AirBnB help you relocate them for rule-breaking, but I don’t know what kind of proof you’d have to have for that either. If you end up finishing the reservation and if the room smells when they leave, I would suggest putting out bowls of vinegar, sprinkling baking soda on the mattress, carpet, and any other fabric areas, and spraying Ozium spray to get rid of any odor.