I'm in agreement with most of the other posters, @Luann13 . My house rules clearly state no smoking, e-cigarettes, or vaping (as well as drugs) on my property. In fact, it is noted in the house manual that if a guest has a need to smoke, to go to the sidewalk or back alley (it is an urban property). There are also no smoking signs posted by all exits so it is a constant reminder!
I have had both short term and, surprisingly, long term guests, who are smokers, but all read the rules and respected them. In fact, a few have visited during our cold, windy winter and still went outside multiple times day and night to satisfy their fix. Another guest collected their butts and threw them away so as not to litter the area.
@Anonymous makes a valid point as well about there being multiple sources of smoke (and other odors). As hosts, we need to be prepared to deal with all kinds of issues. Most times these are easily rectified.
My smoking guests have been respectful and surprised me with trying to honor the policy. Since these visitors have followed the rules, I have never docked them for cleanliness or any other stars. Surprisingly enough, some of them have indicated that they want to return.
Just be consistent about your no smoking expectations with guests and I think you'll be fine.
P.S. Be careful about prohibiting or declining smokers outright. This might be viewed as a discrimination issue by Airbnb.