There is nothing written specific to a real property portfolio trade that I know, but I also do not know of all books published.

It's not the seller's fault if buyer accepts huge monthly payment as a trade off to own the property.

I see stuff trading at a 5 cap in urban core Atlanta which is nuts and I would never touch such investments.

Maybe the right answer is to finance according to your desired out come while affording  a risk factor /growth rate you are comfortable with? 

I never saw the final outcome of any of these (including the auto) so I don't know what final pay out was.

That does not sounds right... your credit score would have dipped a few points each time you obtained a loan application but if you are paying off CC and mortgages (major trade line) there should be no reason for an 80 point drop.

Great outcome @Vicki K. !

If you want assurances that certain items are good/bad/acceptable, you'd likely need to contact the individual trades that deal with each item (roof, foundation, electric, HVAC, etc.).

Seller paper does not trade for any type of premium.

Ask for help from friends who might know about one of the trades (Pay them with beer if you can).