This has been a long thread and has lots of anger associated with it in places. Non smokers can smell a cig butt from 1/2 a mile away, thats a fact.
I'm an ex smoker (going on 4 years now) that isn't really bothered by people making choices to smoke as long as they don't smoke in our rental units or home. Out of 300+ bookings, we only remember 2 that decided our rules weren't applicable to them and smoked inside, it took a little extra cleaning but no other guests ever mentioned any lingering odor! We also live there so if they were smoking inside, we probably would smell it in most cases.
We do encourage smokers to go outside (we live on 9 acres of beautiful lands) and enjoy a smoke even putting ashtrays where appropriate, I believe that has probably helped stop potential rule breaking. If you've never smoked yourself, you don't understand that if your a smoker, you must smoke or you will make everyone around you hate you for more than smelling like a cig butt. If a host doesn't find or have a place they can smoke, you should just say no smokers period otherwise your inviting problems somehow thinking they will not need to smoke while they are staying with you. Stay well, JR