You have to be in the area and know what you're doing and have the contractor who will get things done right. 

As a general contractor, I have a strong understanding of the buying, selling, and financing processes, which gives me an edge in evaluating and improving properties.

I would rather manage my own for all of those reasons but I am concerned about the difficulty of contractors and other services in such a small area.

The advice I give to my clients who are first-time borrowers is to have three people alongside you as you start your path with fix and flips: a realtor, a general contractor, and a lender. 

I need a general contractor in order move forward on my plans to flip, as well as becoming better informed on the what, how and why of the processes incumbent in flipping.   

How can I structure the contract or investor payout terms to ensure they feel secure and confident in receiving a solid ROI?

They communicate with a general contractor so they are confident in what their rehab cost will be. 

Thus, if the owner of their Milw, Class D property replied without noting the above, he/she might say it only costs $1000, whereas the owner of the SF Class A property might say, $10k, but if I didn't know their location, property class type, if they used contractors, or did the work themselves, etc., then I would still have too wide of responses to be able to anticipate what the real costs might be for my particular situation, property, etc.For reference, my properties are in Class B areas of Milwaukee.

You can install a lockbox onsite and place a master in it for your trusted contractors.

If you're way off with these numbers you will go under, and then 2) getting burned by the contractor is a real thing.