Samandriel's motive was, of course, to get Carrick off of him for the time being and perhaps to stoke whatever fire he had in him enough to call him out for breech of contract later. A loophole of his own. It was fairly clear between Samandriel and his Master which of them was the brains of the operation. Beyond that, though, between himself and his sister, his general lack of temper or want to lash out made him a bit of a better fit for the kind of revenge that was actually successful.
He stepped away from Carrick, pulling his t-shirt over his head as he toed out of his loose shoes and took care of the expensive, fitted jeans and boxer briefs Mitchell had gotten for him. Clothing taken care of, he stood proud and strong in front of the ancient vampire.