You cannot take the cost exercise to the next level without starting to get more specific about what it is you're going to build.

This is an eye opening exercise.

You cannot exercise the 30% federal tax credit on rental units. 

Sport, exercise.

At that point, the seller could choose to simply reject the request, in which case the buyer may or may not choose to exercise their right of cancellation of the agreement or simply proceed as previously agreed and eventually remove their contingency.

They gently 'nudge' me by saying "well, when we work for XYZ Inc, they use this system, can we try it for you?"

This was without a doubt an exercise in persistence. 

My guess is they already have a first choice and this exercise is about extorting more money from the preferred state/city.

Property management with that mindset becomes an exercise in bleeding the owner carefully, siphoning off as much as the profit potential of the property as the manager can possibly get away with.

I find the best way to "harden" my rentals is to get a "gentle" tenant:D Try showing up to an applicant's current residence unannounced.