Or for minimal work, drill small holes near the pipe and spray foam insulation.

Soil type, adjacent land and what they have on them (spraying chemicals or not).

The downstairs tenant’s want me to spray insulation in the walls and ceilings as a way to mitigate the noise level and help with the heating costs.

Then she will spray in down with oil to make it easy to pull out on the next pour.

But hard to charge much for one extra coat of spot painting with BIN Shellac primer or the spray can.

So places you'll find them or they'll hide out - wood furniture, bed headboards, under the mattress, they'll crawl to the ceiling/corner of the wall and lay eggs (look for black specks) - if you see things like that you'll need to scrape and paint - there are treatments you can do to spray the baseboards, furniture etc - local pest control companies should be able to treat - I've also heard the only way to fully get rid of them is with a heat treatment as well as everything else I mentioned.Your tenants would need to wash all beddings, strip all furniture down, spray/treat the furniture, spray baseboards, etc etc - pretty labor intensive to do it right.

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.