Do you smell cigarette smoke, marijuana smoke, other odors? 

Ideally, you can just non-renew his lease and get a non-smoker in there, but I don't get the impression you want to be that aggressive yet.

Some places have bathrooms that lack sitting thrones and toilet paper, unless you are in a hotel/restaurant that caters to Westerners (you could pogo stick bounce on one side of this toilet all day and not cause any bolts to come loose):Let's see... smoking cigarettes inside.

I also look inside their cars to see if they are messy or smoke cigarettes.

3. make sure you do not rent to any smokers! 

When Homeaway began to restrict the ability for owners to see the guest's email address or telephone number I was worried that because I could not talk to the guest when they initially inquired (as was my procedure) I would end up having to cancel bookings because the guest might not meet my requirements (age, number in party, non-smoker, no parties, etc.)

And what about smokers?  

Its not cigarettes or pets or body odor or mildew or even simply dirty people.

Never had scented candle smoke damage but I did have the worst smokers damage that I have seen in many years.  

@Megan ThomsonYou know they smoke, they know they smoke but of course they are still going to claim to be non-smokers.