He  lived in unit one and air bnb-ed unit 1's "in law" suite.

Should I insist that the sellers turn them on so I can do a final test of the plumbing, central air, electricity, etc?

Air:  Heating and cooling, what type, all rooms covered, thermostat, window units, everything working, if forced air, need servicing of ductwork, etc. age function of unit, type of fuel used. 

@Joshua Feit my agent just did a 1031 to buy a nice air bnb property in Gatlinburg.

How is the air bnb currently going?

The other thing you can look for here in So Florida, is a 2/2 with a Florida Room that could be converted and brought under air and turn it into a third bedroom!

Another house we were interested in we drove by weekly and saw the cabinets, air conditioner, ceiling tiles, etc. being removed a little each week. 

From what i have learned, gas (pool heating) and electric (summer air at full blast) will probably be more. 

Smell the couches, drapes or anything that may retain smoke smells because they can easily air the place out and mask most of the smell with scented candles, incense, etc.2.

I have now put a plastic cover on it to stop it from getting wet but those lights need air circulation.