I think there's an implication that he did a lot of horrible things in life beyond tricking the devil and that's why he was stuck. Besides, the devil is someone who always tries to win the upper hand.

[Not that he has any first hand experience. He's battled a lot of things but "satan himself" is not one of them.]

Really? That's odd, I wonder what's wrong with her. [He rubs his chin.] You think she might be a ghost of some kind?