She claimed "air quality" and "water quality" problems among her chief concerns.

Your just rambling on and on with wildly bizarre things, plucked from thin air it seems, speaking NOTHING to the actual conversation here. 

Together the portfolio is worth 2.5 Million and he STRs them on Vrbo and Air BnB. 

The air conditioning doesn’t work, the fridge is broken, and the property is far from "turnkey."

I would say air on the side of caution.  

They built a pole barn structure, air conditioned it, strung up some lights and trendy decor and host baby showers or weddings almost every weekend. 

There are several STR's on AiR B&B that do not abide this; are they likely operating outside of permits or does the county make exceptions?

& different parts of the asset can be depreciated on different schedules.To find out the useful lifespan of each component, you do a cost segregation study to analyze all of the parts.The raw land can't be depreciated so you start by giving that a value first.But other items can be depreciated on a quicker timeline.A roof, road, sidewalk, fencing, walls, gates, doors, latches, flooring, air conditioners, pavers, curbing, landscaping, etc.The IRS has a depreciation schedule for each type.Some parts are 5 yrs.

Many properties in Macon lack central heat and air which I feel is a "must-have" amenity in GA.

If mold remediation is done by a handyman without air sampling or post-remediation testing, it can lead to issues during the sale.