But all tenants were and are long term renters.With one, the neighborhood changed (worsened) and he no longer wanted to rent there.One lost her job and ended up having to downsize.One was dis-satisfied with the pest control I provided (I really did try to work with her on it but spraying every single month was simply not an option.)

It'll take 5-10 mins to spray each apartment, and maybe 10 minutes to lay roach bait in each apartment.

Spray it on the stains, give it a minute or two, and spray it down the driveway (not into the adjacent grass). 

So I had an ant problem in my unit while livening there and the landlord sprayed a chemical on the countertops to combat them after the store bought stuff I was using wasn’t cutting it.

If you do decide on doing something, make it something for your benefit-- like leaving drain clog remover, or pest/ant spray, something they can use first instead of calling you.  

The overwhelming response I received was you can do sprays on the exposed wood, try to remove the food source (use composite) or do ground treatments to create a perimeter.

I've found that pests are most often caused by tenants - and if they are clean, it shouldn't be too much of an issue to do an annual treatment in the spring, then maybe give them a gallon spray bottle from home depot to use as they need it.Just like @Joel Owens says - trash bags, eating on the carpet, etc... all bring the bugs.I had a 3-building complex in Birmingham that required monthly pest spray.

Carpet and some sheetrock were removed, surfaces sprayed and basement sealed off and fumigated. 

Here is the link:Maxforce Building perimeter spraying and interior spraying with a long residual is best when used with this bait. 

Actually, the ceiling being painted (especially if it was spray painted) would make the ceiling even safer because if there is asbestos in the popcorn it becomes encapsulated in the paint.