Simply be a calm stand off landlord who is expecting his tenants to honor the lease - Not you accommodate their personal situation.

So first thing, when ever I have someone displaced coming using FEMA money to pay, I'll be doing a full background into where they were living before and contacting their previous landlords.

The way that things like this are typically handled is that if a lawsuit were to happen, since both people have been behaving under the assumption of a lease (the landlord renting their space and the tenant paying rent), they would probably treat it as if there was a standard month to month lease agreement.  

I've been a landlord for 15 years and this question pops up a lot.

Let's analyze each issue you've mentioned:1) Tenancy Length: besides issues a landlord can't control, like death, sickness, job loss, etc., the actual management of the property & tenant play a large roll in how long tenants stay in their home.

I see so many landlords lowing money through rookie mistakes, yet they continue looking for more doors.

I have a note in the lease that they're not supplied or warranted by the landlord and the extent of what I will do (if any exist at all) is haul them away. 

It would be smart to do a full lease audit, estoppels issued, and tenant interviews.And if you are buying cash, there is nothing mandatory, since it is your money at risk. but again, physical condition inspections, understanding of tenants (they are a great source of information about issues with the property that the landlord may not know or may not disclose), surveys to understand accurate property lines, etc.

Or it takes a third week for your new tenant to move in, now your negative $200 if all the previous expenses were paid by the landlord fairy.

Fourth, tenants tend to “try more stuff” with mom and pop landlords than property managers.