Why did Dickens include the episode involving Gamfield, the chimney sweep?

Oliver is confined to a small dark room while the board waits for someone to take him. Mr. Gamfield, a chimney-sweep who is in debt to his landlord and badly needs five pounds, sees the notice for Oliver and offers to take him. The board negotiates with him, and agrees to give him Oliver and a little over three pounds. Dickens is showing just how easily children are bought and sold. He is illustrating how eager adults are to take advantage of children. Luckily the magistrate sees how scared Oliver is and refuses to sign the legal papers.