Reasons for this were conflicts on what was really covered, additional costs or items not covered (replacing a furnace but supposedly additional $1,000 in work not covered), slow response and slower action, and a disagreement on what the right corrective action should be (an AC unit 25 years old where the warranty contractor was trying to clean and say was fine no other problems).  

I'm with Bill Gulley I agree with your points, too, however this investor will get confused as to which side he's working and a DIL may only make it tougher for a clean end play.

.- separation of books/finances/accounting - seems a lot more clean cut with its own entity

It looks nice and clean.

Whatever it is, he gets it at closing after you've inspected that the house is still standing and is broom clean, and like a prize, he must be present at closing to win.... while you all are there signing papers and swapping checks,  you're having someone change all the locks. 

One day I received a phone call from the kid that does basement clean outs for me.

Lock changes, boarding up broken windows, cleaning out junk left behind, tarp leaking roofs, winterization, and fix safety relates issues… Other than that… Yes, go after the Realtor and the Real Estate Investor…

That's exactly my original question: how to find the actual rehabbers (which is what I mean by "end buyer": one who actually intends to fix and flip the house).The obvious things I can do are:1) Clean up the property and make it as presentable as possible without going to any great expense.

well we never had to keep a clean porch with the last landlord"., etc.I wish I had looked more closely and asked more questions when I bought.

What's better then having a property investor who keeps his block clean and keeps his tenants safe?