Such a bored and displeased expression. So it might be the face she's looking at that could be turning her off or maybe she's thinking if it's worth the money for the new Gekota toy. Maybe both.
Even in the world of Hentai I just don't see Mikoto selling her body for money, I'm sorry I just don't, isn't the school she goes to made for rich students anyway?, so Mikoto would have quite a bit of money, she wouldn't need to do this.
*sighs*, Such is the world of hentai, ignoring a characters personality or anything else just to make them have sex or get raped....