We refinished the hardwood floors, and updated the tile and other flooring.

I found very small pebbles in the area next to the sliding door and just one of these could have created scratches like that.My issue is that I have no idea how to calculate how much we should deduct from their security deposit to pay for the refinishing.

I will be having someone look at the wood floors to see if they are worth refinishing to cut costs or not.

He uses that wood looking herringbone style florring at HD. http://www.zillow.com/homedetails/3446-Glendale-Ave-Louisville-KY-40215/73445483_zpid/ http://www.zillow.com/homedetails/507-W-Evelyn-Ave-Louisville-KY-40215/73431857_zpid/ When hardwood exists, might as well refinish it; otherwise do carpet.

They need to be refinished, but I don't think I'd have time to do it before trying to get new renters in because of the vacation situation.

The current tenant has been there for 12 years and it needs upgrades such as appliances, new screen on a porch, paint all around, refinish the hardwood floors, and possibly electrical and HVAC upgrades.How is this best done without flying out there to manage the renovations myself? 

The $20,000 in upfront renovation costs consisted of new windows, kitchen refinishing, password-protected front gate for tenant security, and back entrance facelift.What interested him in the property?

For example: with rentals, will you refinish hardwood or just use carpet?

I doubt your timeline of "a few weeks" works if it involves remodeling the kitchen and baths, other plumbing work, electrical, HVAC, paint, refinishing floors, replacing windows, redoing roof, etc. 

Most of the equity I took out was put back in to rehab the property and redid that backyard/patio deck,refinished the pool, new roof, new driveway, paint, landscaping, resurfaced kitchen cabinets, etc.