Two treatment options:1) They put chemical into the effected areas through holes in the sheetrock.

My thoughts would be chemical, even though that will likely kill it back to the roots, on their side (oh well!).

They start diluting the (expensive) chemicals, and tenants complain that the bugs are out of control. 

We recently turned over one managed unit ourselves and sprayed chemicals, round up and home pest control, right before we left.  

Smoke alarms down like the fumes the Zinsser Shellac gives off so remove them before you apply the shellac so their sensors don't get saturated with the chemical.

If it does come out to be a smaller issue you can look into doing your own treatment via some chemicals I can recommend.I'm near a university and I frequently take my literature or correspondence to the tutoring center with some candy and get students to translate it for me.

Most of those chemicals dry pretty fast, and if it was going to peel it probably would have done so already.

But, if someone was poisoned due to chemicals, you would probably be held accountable as the owner.That is why most states require training and liability insurance to obtain a Pest control applicators license.Think about this: If you need to treat a unit and it will require the tenant to be out of the apartment for a couple of hours, you may want to hire a licensed pest control company for the job.

If you do it right, you should not see anymore in a few weeks.With persistence and a thoughtful approach (as opposed to chemical warfare) you can beat cockroaches.

There are 2 treatment methods...the heat treatment and the chemical treatment.