Go over with a spray bottle filled with hydrogen peroxide and water or bleach and water (the hydrogen peroxide is better at permanently dealing with the issue), spray, wait, show them it's gone. 

(think bottle rocket) There's a lot of volatility in that.

Gallon of bleach water with a small bottle of dish detergent, put into a pump sprayer.The bleach kills the mold and the dish detergent keeps the bleach attached to the walls or beams if you have to remove the drywall.We have used this system over and over, both in NOLA and in FL, where we do the work then call a remediation company to test.  

Going through a bottle of ammonia per room. 

It's a spray that is just a couple bucks per bottle and I found eliminates both smoke and pet smells. 

Ditto Myanmar, from which the genie just left the bottle.

Those are great ideas. we always give the tenant a welcome basket when they first lease the home, Toilet paper, water bottles, spaghetti sauce, sometimes a plunger... just stuff they may need or can use when first moving into the property.. they LOVE these items.. all things you can buy at the $1 store.We also send them a movie gift card and dinner coupon during the holidays and have a hand written note letting them know the owner asked us to send them this and thanking them for being such great tenants.If you are big enough and have enough homes you can normally go work a deal with a local restaurant to be able to get some discounted price off the coupon value if you buy quite a few of them.

Depends on the level of deal we´re talking about here, but with something like that $30k victory you´re celebrating I´d probably buy the bottle of 1988 Rémy-Martín Vintage Premier Cru I´ve wanted for a while, and enjoy that with a 2007 Trinidad Ingénios Edicion Limitada cigar.

Bottle of paint?

I've seen at least one mention of this, but I used fabric softener mixed with water in a spray bottle 50/50.