What kind of credit score do they have, and is it high enough to meet the requirements of lenders?

Asking for POF (lender pre-approval, bank statement, line of credit etc) for a property like you have is perfectly normal. 

You go in front of a judge they appoint a trustee and you make scheduled payments usually smaller than the previous payment until you get caught up and a head.In most cases you can rebuild your credit scores while you are making payments back to the trustee.

Or are you looking to track expenditures for bookkeeping reasons?

Also no one with felonies, evictions, or credit under 650.

Some of our local banks and credit unions have great deals - much better than national lenders.  

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

I explain they will have difficulty renting a quality unit, that I will ding their credit, that I will attempt to garnish their future income to recover what they owe.

I'm looking forward the data analytics page getting built out fully; the beta version shows promise.The fees for credit card payment, using FF affiliate KeyCheck, are higher than most of our guests want to pay.

A lender would have to be a fool to lend on collateral that wasn't protected - if the house is lost in a fire or whatever, the loan is unsecured at that point and is basically credit card debt.