Like many (most) businesses it requires an investment of capital; money expenditure for ongoing marketing; management of operating, marketing and professional personnel; keeping accounting records and filing tax returns; established sales practices; constant monitoring of goals, budgets, and productivity; establishment and implementation of operational systems; and providing customer service.  

They may have a separate system or entity that is used for holding properties vs the business itself for legal protection.

The GIS map designates it as a single-family dwelling, but the property is clearly set up as two units, with separate HVAC, electrical systems, etc.My main question is: Would it be possible to obtain a permit to legally convert it into a two-unit property?

This will help you to build your systems out as well.

I would love to hear more info What did you learn that is not available for free on the Internet?

Quote from @James McGovern:One of the problems with the new system is no transparency, so will be tough to know if commissions were negotiated?

Get an STR property management system like Hospitable to help automate a lot of things.

The internet books Morby the sub 2 guys the market for this is quite thin."

Now for the next hiccup, spoke with the health department today, they are saying the entire septic system will need to be replaced because of a change of use.

People sit on the internet and think they are learning, not happening.