Check the application against all of your other screening criteria before entering the murky waters of a service animal. 

Make sure you can add value to it, don't overspend, cash flow positive each month, look to purchase in a good/up and coming location and screen your tenants really well.  

You make your money during the screening process.

I would just politely tell him that you screen very diligently and tell him what your criteria are and that you have just as much interest in getting a good tenant as he does in getting a good neighbor.

Nuisance things: paint, wallpaper (very annoying), holes in drywall, smells (unless it is a sign of mold), cracked windows, missing or damaged screens, no GCFI, flooring, broken handles, damaged cabinets, interior doors on exterior entrances (I see this a lot), bowls under sinks to catch leaks, general run-down-unlovedness.

Found our own handyman to do remodel work which is high quality and affordable.

Not a high supply of quality rentals but demand is there.

Tell your friends, family and business associates about my quality personal service.

@Jacob Brattainif the lot rents are that low then that is a reflection of the quality of tenants inhabiting that park.

A lot of high quality investors and real estate professionals in general you would add value to.