"Why should I? What's in it for me?"
"Your bargaining posture is highly dubious, but very well. I will provide you with a new body and new troops to command."
"And?"
"And nothing! You belong to me now."
"I belong to nobody!"
"Perhaps I misjudged you. Proceed, on your way to Oblivion."
"Argh! No! No, I accept your terms! *more screaming*"
"Excellent."
Yeah, that almost works for Mass Effect.