He purchased a lot of real estate for well below “fair market” value.Now, since Helmsley was operating in the NYC market where he was a well known “player”, once his reputation for not negotiating became well known people wanting or needing to sell began accepting his offers in volume.  

We are already seeing small landlords sell and bigger players come in and buy. 

Not doing business with someone because they sent you an email or a few negative online reviews (especially when they are a big player in a market) seems pretty short sighted. 

You have to think about where the opportunity is and where the big players haven't gone yet, while still being big enough to satisfy a bank's underwriting needs.

Find the dominant wholesaler in your market and offer to birddog for him or her.  

I have nothing to add to the thread except one of my favorite basketball cheers of all time is although I was a toddler Austin Peay had an All-American player named James Fly and their cheer wasFly is open...Let's go Peay

The Structural engineer and especially the Architect will control the majority of the cost on the design side, and the Concrete and Framing subcontractors will drive most of the cost on the construction side, so the more you work with these key players, the greater you will be able to rein in costs on the project and the greater the return on you investment will be.

I also haven't read this entire thread, just the most recent, so I can't agree or disagree, all I have done is to express concerns due to the abuse of some gurus and novice players. 

@Dominic Battezzato Perfect, I'll definitely reach out as we move forward.

The best resources for this question are going to be in regions where the ADU has been embraced as an innovative way to create more places for people to live: the Pacific Northwest, specifically Portland, are the key players here.California is not too far behind because the state has made it much easier to permit an ADU through laws, including the latest in early 2020.The basic answer to the question is a permitted ADU should add 20-30% to the value of your property.