[I mean... Sebastian is happily contracted to a master already, otherwise he might feel threatened by this ~challenger~ moving into his Will Grant Any Desire business territory. That's a possibility.
There's also the possibility that he would remain remarkably non-threatened. Sebastian doesn't have a high opinion of gods, but this is so pathetic he's willing to believe not even a god would sink this low.
Also this is the, what, fifth business card that's see-sawed down to land on his shoulder today.]
Sir, I believe this is quite enough advertising. Wouldn't you say?