Dropping the pretense.
Tom is powerless to struggle. The huge man towers over him, holding Tom effortlessly. Tom catches his breath, "Ok... Just drop the act. I know you're a bad guy."
The demon cocks his head, and with a knowing grin replies, "So, what gave me away?" "Well, for one thing... This is a ghoul infested desert, and you're completely unarmed... See that thing?" Tom points to a quasi-human monstrosity cowering to his left, "*That* is clearly something to be afraid of. And it's petrified of you." "And yet, you seem calm..." "Well... I have something of incredible value to your kind." This catches the demon by surprise, "What could you have of value to me?" Tom hesitates, "My soul... My *willing* soul."
The demon crouches, and produces a small bluish campfire. Gazing across the fire, he eyes Tom warily. "Clearly, you know I could steal your soul." "Yes... And it would be worth much less." "So... You offer your soul for?" "Well, I'm not offering *you* anything; I seek the One that has imprisoned my sister."