Face it, Airbnb is a bookings broker. They have Terms coming out of their yin-yang, but because smoking is a he said-she said situation, they appear to be absolving themselves of this one, too.
I found the best way to deal with them is acceptance; specifically 2 convenient and comfy smoking areas. I guess they will be wanting them covered and heated next (!) and I ask them to wait a minute or two before coming in. So far so good.