On the other hand if they are a sponsor that is experienced in stopping a skin in the game, that's a huge red flag for me.c) how open to scrutiny are they?

Clothing- buy at the second hand store.  

. - Fortunately, our transparent systems allowed the owner to catch it:)- Full transparency - we would have never caught this honest mistake:(An owner also needs to be involved to approve & fund large expenses: maintenance, property tax & insurance payments (if they want to be more hands off), evictions, etc.A great PMC should also have a chat with you annually about your future plans for a property and your portfolio. 

I can show you how to do it (holding 'dozens' of deals' in his hands.)  

On the other hand, true private lenders are not professional lenders and hedge fund type lenders (which is what hard money lenders are), but instead are regular people in your circle and sphere of influence.

In most single family zoned areas adding a single ADU is not a value add meaning it will not add more value than the hands off cost of the addition.  

When we order an appraisal, we are handing in a rehab budget to the appraiser and they will use this to help calculate an ARV which is used in the lending calculation. 

My contractor has gotten impatient waiting for him and has started taking matters into his own hands (he did the jack hammering of the floors which my plumber said had "complications" and would "take forever to get through"). 

And here is a key thing, early into it for discovery conversation I ask "If I buy this, let's say at $____, and I pull up a brinks truck at closing handing you bags of cash for it, do you have any use or plans for where you'd put that $ now?" 

This includes if the property does not close.Your agent should be holding your hand through this process.