@Alex P.Here's a few references to start that may help you to find the answer to your question: Treasury regulation §301.7701-(3)(b)(1)IRS Private Letter Rulings 9807013, 200732012 and 201216007If you need help finding these or interpreting them, as well as knowing how reliable they are for you to use for your own taxes, consult a tax professional. 

I actually during the credit crisis when our PDX banks froze  ... contacted them about doing a subdivision A and D loan for me... sent docs down  but I got a pre qual letter to quick and what I thought was too easy... next step was the 10k for due diligence, being a lender myself it was just too easy...

Maybe just a stern letter from an attorney will be enough for the sellers to come to an agreement to pay something to you without having to take it further. 

Off of the purchase contract, I would verify proof of funds, ask for prequalification letter from a lender if buyer is receiving a loan, with a good faith deposit.

If they refuse, then send a demand letter.

I think you are on the right track comparing options - however I would note that there isn't really a differentiation between "DCSR" and "ARM" - there are a lot of 5 Year ARM options for DSCR Loans so theres overlap - maybe you are referring to a true 5-year balloon bank/credit union type loan?

From there, I hand wrote letters to distressed owners of properties, and did some fix and flips. 

This amount is fully refundable for any reason if you do not execute a loan commitment with us and you request in writing within thirty(30) days of the date of this letter the return of the $10,000.signing of the loan commitment, a commitment fee equal to five percent (5%) of the Financing Request is due; three percent (3%) would be payable at the signing, and the remainder would be payable from the loan proceeds at closing.

Ignorance of lead paint presence doesn’t exempt you—you must have a compliance letter to avoid strict liability.If you rent to a couple or a single woman and she becomes pregnant, the law requires you to delead the unit.

Off market deal --> send a letter to the landlord who owns the house outside their state.