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. 

If the rental comes with central air then you could install a more expensive air filter and also maybe run some air purifiers or a mold fogger and see if your cough improves.  

Hmmm . . . )I also change the HVAC filters every month myself.

Another decent indication of whether a tenant has been smoking will be the air conditioning filter.  

And forcing them to call - which may actually be a good thing to filter out time wasters.

If something needs to be looked at, I do a quick one-over look while I'm there - mostly checking HVAC filter, floors, and under sinks for leaks.

I tried to Amazon my tenant air filter 3 times a year. 

The smell is easily handled using a carbon filter, and it doesn't stick around after the plants are gone (the smell from smoking it is a different story, of course). 

3) Landlord and personal references – filter through these.

My point here is that yes you can feel bad for a tenant who has fallen on hard times- but it’s important to filter the situation to a non-emotional, stark reality.