Thank you @Matthew Irish-Jones and @Ryan Howell for the feed back so far. I like the idea of transparency where this is concerned. As an investor there is little incentive to pay market value for a property as the goal is immediate equity and cash flow.
However, an investor does provide real benefit to the off-market seller (especially one experiencing personal or property distress) in terms of an all cash offer, closing without contingencies, taking care of the rehab, eliminating the need to list the property, etc.
A seller who is in financial distress may not have the time or desire to list the property and wait for offers as their timeline for losing the home may be short. In addition, if the property is in distress and the homeowner isn't willing or able to rehab it they should expect the person who is willing will want to be compensated for their time.
I could still see a rare scenario where the seller could come back after the fact regretting the decision and try to misrepresent what conversations actually took place. Even though you were transparent and laid out all of their options for them I think you would have to find some way to get an independent 3rd party involved in the dialogue in order to more fully protect yourself against this.