My T never goes over, but my marriage counselor sometimes does, up to 20 minutes over (today was 10-15 extra minutes). He never charges us for it, though. He tends to give us more time if we're on a difficult topic (or maybe if his break is right after the session, which I think was the case today because no one was waiting for him after). There was one time he could only stay for 20 minutes because of an emergency, and he didn't charge us for that session.

I think if you're not requesting the extra time, then it's unethical for your T to charge for it. If he was like, "We're out of time, and we could stay longer, but I'd have to charge you extra," that would be OK. Or if you had discussed it in advance about payment, and he let you know when you were approaching that time. And you said, "Yeah, I need those extra 15 minutes today, so I'll pay." Then it would be OK. But not so arbitrary.