While I agree that it's the middle person's choice, that doesn't mean the AC people can't influence that choice. They don't have to open the discussion with "would you like A or C?" If they prefer, say, AB, the C person can simply ask the B person if he or she would like to switch for the aisle without mentioning (yet) that the window could also be an option. Most will switch, since most people consider that an improvement. If the answer is "no," they can try offering the window to see if that offer gets better results.