And we all know how cigarette smoke clings to everything, including the smoker, so certainly the apartment's smell is not evidence of smoking.I don't want my tenants smoking in my building, but I'm not sure that such a restriction is enforceable.

I even had criteria that would get a tenant denied like: rude behavior, came with rude friends, showed up late without calling, missed an appointment, didn't fill out application completely after being asked to do so up front, smelled like cigarette smoke, had filthy car, just on and on. 

But during my inspection and walking of the place prior to close I can smell the strong odor of cigarettes and have seen the ashtray in his apartment.  

But, you'd be amazed at how someone supposedly broke finds money for new cars and cigarettes and the casino, etc.  

We don't smoke cigarettes. 

I had a Section 8 tenant who smoked something in the bedroom (whether it was marijuana, cigarettes or something else, I don't know) and two of the walls had what looked to be watery light-colored tar running down the wall and so smoking does cause damage. 

Again whatever you feel comfortable with in terms of escalation here.No personal experience with this device and not sponsored, but I've looked into FreshAir Sensor previously for my Airbnb, and it is a simple plug and play device that detects cigarette smoke.

I clearly did have that part in my paperwork that one could not smoke in or on the property, and I saw massive butts on my porch and charred black marks where she put out her cigarettes on my cedar shake siding.

Our nightmare tenant also resulted in other tenant complaints, cops being called for noise, parking crazy in the parking lot taking up two spaces, destroyed carpets where they let cigarettes fall and burn on the carpet (and smoking wasn't allowed), her baby daddy moved in almost immediately - it can result in lots of time dealing with complaints and problems and I almost lost good tenants, too, who I had to assure I was getting rid of the nightmare tenants.  

I stopped eating out, I quit cigarettes, I educated myself, I cancelled memberships I wasn't using or could go without, I stopped buying clothes that would eventually end up in a donation bin, and I stopped sitting on the couch when I wasn't at my W2.