Since this is a rehab, you shouldn't have to worry about offering a builders warranty but here's some things I've become accustomed to doing to make the warranty, sale process and transaction process easier.  

From a transactional cost standpoint alone, the fees on the way in and on the way out require significant appreciation to break even.

I understand they purchased their property bit earlier at a lower price, but the difference shouldn't be so significant.

If you are having that much activity but cannot find the right tenant than you will want to lower the price just slightly to entice better tenants OR you can relax on your qualifications.

Could you not put a lower amount down? 

You may FEEL that they are but your expenses may go UP at the same time as rents need to be LOWERED!

I would not put so much on an appraisal report.A number of reasons might be the answer for this lower appraisal report:1- What city is this property located?

Which is why I pay more, for less cash flow in highly desirable areas.In high income areas, rent is a lower proportion of income so therefore your tenants have a higher capacity for paying higher rent because rent is less than 20% or even 10% of their income.

You’re able to learn the basics of a real estate investment with lower risk and build equity at the same time.Because you're in the military, you'll be able to enter a property with 0% down which means you can leverage your money way more effectively. 

We took the reverse action and started lowering asking rents until they moved.I suspect the reason that one property of yours turned quickly is because your asking rent was very favorable vs. local competition.