She wrote on the wall herself and spray painted over it. 

For sealing in stains like that (if is from smoking), use spray paint and then normal paint over top. 

A cheap solution would be to buy some bed bug spray from the hardware store.

Duct tape, spray foam, and endless tubes of caulk make up the material list used by repairmen and property managers from years past.

I have spent ten years assemble a team of great subcontractors and I still find myself looking for new specialists all the time - for example a waterproofing contractor; I did not even know that someone would make a living of just that; they did nothing else than spray the outside of the basement walls with tar and when the bill came I thought they had missed a zero - it's ususally the other way.Here are my two favorit ways of finding contractors.1.)

A couple that come to mind are the house where we had to spray the wall with lysol and use a scraper to get the smoke and nicotine that was oozing off the wall or the place where dolomite was spread everywhere to control the fleas, or the place where the renter cut a hole in the floor and put the drain hose from the washer into the hole to drain under the house or the one with the rotted hole in the kitchen floor that you had to step around to avoid going through the floor, or the one where it took a full day just to scoop the dog poop from the floors and use kilz to cover the dog pee, let alone the back yard, and on and on it goes.

Not only did it have all the stuff covering the floor, but the entire interior had been spray painted purple and black stripes (obviously during some drug binge).

I thought you may have had some "tenant be-gone" spray you could share.  

For an aerobic system you need around 5800 sq ft for the spray area for 3 bedroom home.

Pet stores sell non-toxic, fabric-friendly flea spray for home use.