I am getting very close to turning off the instant book feature. I took one step closer by adding that instant bookers must have a review first.
According to a google search, as a landlord you have a right to keep your property smoke-free but this may depend on your state law as well:
"Because smokers are not a protected class under federal or state law, as a landlord you can refuse to rent to smokers. In other words, you can reject an application if you are told that the applicant intends to smoke in your rental property.
So, if you are interested in keeping your rental property 100% smoke-free, it is not illegal for you to refuse smoking tenants. It is your right and responsibility to set up and maintain your property the way you want, as long as it is legal."