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

Verifying last 2 years of rental history very important!

When the “guru” himself does not have a verifiable track record of success in the very thing he’s teaching3.

Let them know you will inspect to verify.4.

Like I said, verify the disability first!

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

You can choose to terminate their leases and start fresh, or verify their ability to pay the new rate.

If you are trying to buy a bank owned property you just send them the contract they want you to sign and proof of funds, or if you have financing, the commitment from the financier, who may also have to provide their own verifiable proof of funds. 

If you total monthly rent is $1,000 (you should verify) with a property value of $145,000 may not work in order to cash flow.

I wonder if you got in touch with Amex and verified everything beforehand and had them reach out to closing attorney if that would matter.