So what constitutes my paying hundreds or thousands of my hard earned money on a single seller lead? 

If this is a small slice of property that hasn't been used by the claimant or his predecessors for 30 years, then a lawsuit against you is unlikely.But if you are sued, then based on what you've posted, you have a valid (legally cognizable) defense.  30 years of continuous use of the property by you and your predecessors constitutes (Adverse Possession and/or Prescriptive Easement). 

It has been 3 years since we left and we've been lucky to have some friends stay in the house who paid us some money but nothing that I would constitute as rent to appease an investment property. 

(I am an attorney, but this does not constitute legal advice.)

Material misrepresentations or omissions on the Application will constitute a default under the Lease or Rental Agreement between the parties.

I know the basics, but what criteria and metrics constitute a strong market for your, personally?

All the above posts are correct however I'll add this: What constitutes a "bedroom" has nothing to do with the building department (generally).

By doing that you can start to get familiar with the different price/rent ratios of all the neighborhoods and what constitutes a good deal or not.

There are protests for about everything else; maybe it's time for landlords to exercise our constitutional rights to due process of law ?!   

I was waiting for the punchline about what constitutes "haunted" ...