Unknown people on the lease?

What about all the unknowns that pop up and throw a curve ball at the most sophisticated & experienced investors.

I've looked into advertising on zillow/realtor, Facebook and other sites but with no experience I'm not sure on which one or if any is most beneficial for a new realtor at a relatively unknown brokerage.

My goal is to be able to buy single as well as multifamily homes and live off of the rent (long term goal) Ive also met with a broker who works with short sales, he takes on about 10 "projects" a year presents you with the short sales in area of interests (mainly Long Island) along with high and low comps, he asks for a percentage (unknown, at our discretion it appears) of the  profit after the property is sold, he typically works with investors who buy and flip. 

The thought of doing a 1031 exchange came into my mind, but I'm cash flowing really well on that one unit I have and the fear of the unknown scares me a bit. 

and some fear of the unknown from my spouse. 

Your $345,000 house will be worth $200k by the time the unknown tenant buyers get done with it and you've had to foreclose on whomever he's assigned it to.

Only real potential unknown for me is investing in a non-elevator building and unit is on 3rd floor.

This method leaves a lot of stress and unknown factors off the table and limits the pool of potential buyers to serious investors instead of dealing with the potential issues of individual buyers looking to buy a owner-occupied unit. 

I declined as I'm not going to commit to paying an unknown amount.