If a model tells a member she would never date anyone off the site, she is not misleading him. But some men love to fantasize about the possibility of changing your mind. As long as I do not feed that fantasy by making it seem like I would date them, there is no harm done.(***)
Your idea that a room of 1500 strangers and lucky loos are somehow entitled to know the details of a model's personal life is so fucked up. Models can choose to disclose that information but it is always the models choice. A model might even lie to her room and tell everyone she is single when she isn't and that wouldn't be unethical because it is her personal life. She also lies about her name, the city she lives in and a million other things. It is her *personal* life.
Personally I don't lie about my relationship status be it single, taken, or casually dating. Deflecting the question with humor and keeping it really vague works best for me.
(***) Most of these men would be petrified if you were to actually go through and ask them to meet you. They don't want to. What they like is the fantasy because it takes no effort on their part, they are never at risk to be rejected so as long as it remains a fantasy they have no risk, nothing to lose. Tokens make these guys feel absolutely desired, and this is a fantasy that many are willing to pay a lot for. That is what I meant with the big tippers being into these fantasies. And obviously they do get pissed when they find out their favorite model is dating someone else because it kills the fantasy.