Also, I wanted to hear their conversations to learn things about why they were looking for a place to rent, do they fight with each other, do they smell like smoke or pot, did they bring friends with them who are people I wouldn't want hanging around on my property, on and on.I know some people think having an open house generates a type of bidding frenzy, but you're still going to have to screen them.  

If you are willing to evict for this type of lease violation (smoking in the apartment), what evidence of smoking can you take to court?

Have your father in law go in with proper notice to check the furnace filter or smoke detectors and take a look at the interior, hope he has keys.. have him take photos of inside and out. 

But honestly, besides the occasional light bulb replacment, smoke detector battery replacement, HVAC filter replacement, your monthly repairs isn't all that much. 

My GC just notified me that the Baltimore City electrical inspector wants him to install (a) hard wire smoke detectors, (b) GFIs, and (c) replace electrical wiring in the entire two-unit building.

That alone means anyone can set-up a class and get a book deal just alot of smoke and mirrors.   

We schedule quarterly inspections to check the fire extinguishers, smoke alarms, air filters, and leaks under the sinks, which helps mitigate problems that would affect the health and safety of the tenant and costly repairs for the owner.  

A person walking their dog at that hour called 911 to report smoke billowing out from the roof. 

Pre-screen with lots of questions about how much they smoke, how many animals, etc.   

Wife is always right, and turned out to be a party girl, but the worst part was exactly one week before she left on her lease and graduation, I strolled by the neighborhood and saw her smoking on the porch.