No air quality test yet but that may be a good idea.A few years ago, used a spray gun to paint a room, refinished a table and sanded steps.   

Refinished floors, new windows, replaced roof, updated electrical, updated plumbing, new hvac, new water heater, and punched out back of house and added walk out deck.

Planning on charging 100% for this repair cost, and eating the cost for refinishing the rest of the floors with normal wear and tear.8.  

Its 5 bed/3bath that is completely refinished that could rent for 6k per month.

To sand and refinish the floors would cost the same as putting carpet down about $1600. 

Renovations include new kitchen/ss appliances/custom cabinetry/granite countertops, 2 new bathrooms, freshly painted throughout, new carpeting, refinished hardwood floors, convenient laundry hook-up on the first floor, new plumbing, updated boiler and hot water tank, new electrical, new siding.

If you haven't already refinished the deck, then I would probably go with a complementary, but contrasting color to the siding. 

With wood floor it could be damaged badly enough that it can't be refinished to hide it.

What added more value to this property is that I re-finished the basement by turning it into living area: new windows, outside door, new walls and flooring.

A flipper would remove walls make it an open floor plan new cabinets granite, refinish the floors, paint, etc. etc, but a buy and hold would just do a carpet clean and put a tenant in there.