For commercial properties, I agree on keeping the debt 50% (or 70% as long as you have a healthy reserve level to factor in the longer vacancies). 

As a scientist, I have a healthy dubious relationship with data and all the wrong directions it can send you. 

More frequently I will see deals go at or around 76-79% and investors are still able to make a healthy profit.

The issue was they were using a crooked Appraiser, who was producing much higher appraisals than what the properties were worth.

I personally would recommend getting your license because you won't have to rely on anyone else for running comps or putting in offers.Lastly -- Passive real estate is an overused phrase for people who only want the benefits of real estate and not the work that goes into actually building a portfolio that produces that type of income.  

My low end rentals on Maui produce an average of 25% COC returns, plus appreciation.

I set up all of my properties as buy and hold income stream producers.

This is the method used to value income producing assets.

Plenty of part-time agents (or non producing...) 

They produced great dividends, but I wasn’t combining that with a market analysis.