There are plenty of different reasons a place can stay vacant that may not be realized righy awat.

The reason why is those who tell you it is passive are not being honest.

Three times usually works if your demand is reasonable and the tenant feels an obligation to pay you.

Not sure of the rules if they move out early for a voluntary transfer versus being shipped out for war reasons.

I personally took the classes to get a license and was planning on actually completing my license, (though never did because I moved to CA), in MA for a few reasons. 1) The cost was low, I think I only paid about $400 for the course.2) The time commitment was low, you only need to complete 40 hours of instruction.3) If I wanted to get a license, I could do so and hang it with a broker simply to help myself with my own process of accessing the MLS and being more self sufficient.Having completed the course I can tell you that you will learn nuances to real estate that you didn't already know. 

There is a reason most banks will not lend money for properties under $50K. 

If you don't raise the rent at this juncture and/or offer a new lease/rental agreement with better terms, they are likely to agree to abandon the old agreement and enter into yours right away.Set a reasonable time-frame for periodic "maintenance" inspections. 

Flood Insurance is fairly reasonable if the property is not in a high risk flood plain.

The other good reason to have a Real estate license is if you are a Property Manager and lease units you also may be entitled to extra compensation while collecting a paycheck (for now) and gaining experience.  

You can also reach out to an agent and run your plan by them to see if its reasonable to get a $150k 4bedroom house using FHA.