I had a cousin killed in a armed robbery. He complied and handed over the cash, only to be shot and killed anyway.
Just because money is handed over does not mean the robber will not shoot anyway.
Another thing that has not been mentioned is, what if there is another concealed carry in the store. Say, you are behind the bad guy, drawing your gun. the other person can not tell if you are actually aiming at the bad guy or clerk. What if you get shot by another concealed carry by mistake.
There are too many what if's. you will probably only have seconds to react.
Kind of what I said earlier. The perp may have an lookout, shooting the person wanting to help, or like you said, another CCW thinking something different.
Bad deal any way it goes down.