Thats how I would negotiate i. 

My idea here is to either negotiate a % of back end profit or settle on a set fee. 

Also the person handling the estate is dealing with her lawyer and I dont think her lawyer will advice her accept the contract that says "Assignable".So what I do I ask the buyers- rehabbers to come with me to the appointment and they do all the negotiations.

You still have to negotiate with the owner for a fair price.

VCs are negotiating hard for lower startup valuations in 2016, including down rounds (which kill employee morale and are founders' worst enemy).

Investors that do not add value through creative negotiations, rehab, financial restructuring, or/and good management, etc...will never generate the best returns.  

as a rule commissions are paid by the seller but not all listings are the same. some sellers may have negotiated a lower than 6% commission.

Given the situation, he offered to quit claim the property to me (for a fee) so that I can negotiate with the bank directly for a modification.  

I would recommend cash for keys but be tough in the negotiating.

Don't waste your time doing this ahead of time when you don't know if you are able to negotiate the deal.