@Alexander Wardell it's good to have a contractor or 3 on your team, but a simple way is to reverse engineer and track what fixer-uppers are selling and reselling for for and what profit rehabbers like to make. Example, see a home bought by a rehabber for $100k, sold $200k 3-6months later and you know they like to make 30-50k/flip. Use MAO formula with a tweak as a baseline. Instead of subtracting repairs, subtract the original purchase price. (ARV x 70%) - Price, so ($200k x 70%) - 100k = $40k. That $40k is an approximate number for the repairs and the remaining 30% is profit and holding costs ($60k-recording fees, attorney fees, tax stamps,utilities,interests,etc.).
In reference to assigning, @Charlie MacPherson is correct. You can not market to sell real estate you do not own, but you can market and sell your rights in a contract. It comes down to disclosure and intent. If you plan to assign your rights in a contract, that's all you can market. You can not show pictures of the property, because the property is not what you are selling. You are selling your EQUITABLE INTEREST in a contract to purchase said property. Talk to the attorneys of the big-time rehabbers in the state and/or at the REIAs they will say the same.
Disclosure: I AM NOT AN ATTORNEY NOR DO I PLAY ONE ON TV. I AM NOT GIVING LEGAL ADVICE AND YOU SHOULD DO YOUR OWN RESEARCH AND SEEK YOUR OWN LEGAL COUNSEL