I am constantly speaking with doctors, attorneys, business owners, who have plenty of investable income but do not want the hassle of dealing with RE.

I screen well but I also don't get doctors and business professionals renting from me in my demographic.

As an example my doctor clients make 1 million plus a year income.

There is a lot of medical data available on the internet, yet doctors will not become obsolete. 

Bought a house from a doctor and our termite company found active termites and damage and his company was known for being slack--but they'd been inspecting his house for 10 years.

But you can (a) ask them what their disability is (if not readily apparent), (b) require a letter from their doctor stating that they are treating them for that disability AND that the ESA is part of the treatment.Or just force them all to use petscreening.com to do the verification for you - free if it turns out to be a valid esa or service animal, if not, they pay the verification fee (and you can then charge security/animal fees and rent).

There are also sophisticated private lenders (lawyer's, doctor's, and other wealthy individuals) that lend out their money.

My wife is an active duty military doctor and I am a veteran myself. 

Is the doctor about to retire or is it part of a much bigger practice?

My first guess would be a doctor or dentist or lawyer who needs tax write offs.