I would fly to the area to meet the providers, I would make sure the properties aren't in war zones (even if the cash flow looks great), I would manage the property managers, I would hire 3rd party inspectors, look intensely at school districts, industry, crime, etc.3) Wait until I know where I am going to be for a long time. 

A hydrostatic plumbing test is recommended to be performed by a licensed plumber post Foundation work.

(I.e. inspections, radon testing, number of smoke alarms per unit, etc).Thank you!

Because one of the pillars of the “Howey test” is that the profit derived comes from the “efforts of others.”

Kind of like a test run before doing it on a large scale property.

BRRRR is capital intensive so you will either need some cash or access to it.

It might not be as intensive as many small businesses, which is what I think makes it attractive (as @Erik Whiting said it can be done in spare time) but it's not truly passive unless you do nothing but own the product.

My situation is that I am a Licensed Landscape Contractor in Cali (2017), a recent General Contractor in Oregon (2019), and and just got certified in Backflow testing and repairs. 

The plumber is full of crap (no pun intended😜)  because you can cap toilet flanges - it's done all the time to pressure test new drain pipe plumbing.

You also have to meet a self-sufficiency test, which are strict regulations regarding what the property looks like and how you will pay for the property if not all units are occupied.