Are wholesale contracts assignable nor transfer in NOrth Carolina

[Terrance Merck]

I wholesale property in North Carolina. I recently placed a 4 bed 1 bath under contract. A real estate agent responded to my advertisement and agreed to buy property. I explained to him that I currently have property under contract and that I am wholesaling property. I sent him a copy of my purchase and sell agreement along with assignment contract for his review and signature. He informs me that he does not think contracts are assignable nor transferrable and would rather use NC standard purchase and sale contract and deal directly with seller excluding me from deal with a verbal agreement from seller to pay anything above agreed sell price. I have used same contracts in the past with success and no problems. My question is are sell and agreement contracts assignable and transferrable in NC? I am almost certain I am correct but would welcome insight and advice from all. 

Thank you