He chuckles softly, pleased that she likes it. He casts a glance around the room, but apparently deems it clean enough - and why wouldn't it be clean, when Sebastian is the one deciding how the room will look? - since he puts the feather duster away a moment later.
"It sounds somewhat arrogant put like this, but I am rather good with people." Figuring out people's likes and dislikes, their desires, their secrets... it's what demons do.