d) The people in the crowd understood Aunt Marthy should have been set free.
The passage mentions that Aunt Marthy's mistress had promised her freedom and that it was well known among the community that she was intended to be free. When Aunt Marthy was put up for sale, the crowd expressed their disapproval, calling out "Shame! Shame! Who is going to sell you, aunt Marthy? Don't stand there! That is no place for you." This indicates that the people in the crowd recognized that Aunt Marthy deserved her freedom and they respected her. As a result, no one bid above the $50 bid, and her wishes were respected.
