Are buyers/investors picky and particular about what exact parameters house falls under, regardless of how good of an investment it is based on verifiable (not inflated) numbers and metrics from data sources? 

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

And if I am paying the tenant anything, I pay them after I verify the work meets my satisfaction.My most likely reaction to their reqeust?

But it's like requiring a release for a mortgage 3 owners back that has a verified $0 balance.

On one of them I verified it was going into the storm sewer by putting a hose into it and then Listening at the sewer grate on the edge of the curb.

There is no official "Airbnb license", they don't actually verify your ownership of the house.

So my advice would be to verify the rental market for homes in the same price point as yours.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Lenders will want to verify your income, debt, and credit whereas on a Hard Money loan, lenders will qualify you based on the deal itself and your experience.  

Within 24 hrs of the negative review, Relay reached out to me and requested recent bank statements from my source account to verify.