We agreed upon an under the table type thing since it was off MLS and I signed a termination contract?)

If you have a w/d spend a few more bucks for stainless-steel hoses and a water monitor/shut-off.

biggest unseen expenses I can anticipate might be floor joists, electrical, plumbing (it's got public sewer and water), and perhaps just general full cosmetic replacement if the tenant moves out.

it keeps the highest and best from leaving way too much money on the table.  

Fixing a gas leak on water heater $110.

Not being able to soak an arm or a leg in hot water in my home isn't acceptable.

They also ran some plumbing out from the corners of the home to run all the gutter water out and away from the foundation.

The only other idea if the ozone machine doesn't work that I can think of is calling a water damage / smoke damage restoration type company. 

My partner and I are in negotiation for a 6-unit property in NE Ohio, below are details: 4 rented, 2 vacant / average rent $735 (4 rented units $720, 2 vacant $775)Owner pays water, sewer, trash2 br, 1.5 bath, roughly 900 sfGarage with door + extra parking areaRoof in good shape, air and furnace in good shapeRealistic gross all units filled: monthly $4,400 / yearly $53,000We walked through both vacant units, very clean and basic.

Definitely check all windows, ceiling, roof for water damage.