Obi-Wan watched as he dismantled the saber from his hands. He was staring intensely, his eyes dark, but not angry. He was thinking. "Training is more than parlor tricks and dueling." Ben was careful with his words as he spoke, not wanting to promise anything to this sith. He could prove dangerous.
"If I were to agree to train you, there must be rules." His words were chosen carefully. Very, very carefully. "You understand I cannot trust you, yet." And he understood the rules of two, but he still considered the man before him a Sith in all other ways.
Maybe a child, but a dangerous one. He'd learned he would have to be careful.
"I've seen one turn from the light side with far less darkness in their eyes before I ever came here."