I think most subs "expect" to climax at the end of the session. I don't like for My subs to "expect" anything and I have taught them this in many ways.

Electro and vibs (and even the Venus used correctly) can numb the area from over stimulation and prevent an O - no matter how hard you try.

My policy, if you will, is that you must have permission. If you have an accident, the best punishments I have found are post O torment or forced c.e. - whichever the sub finds most distasteful.

If someone I have never seen before asks Me directly if O is allowed, I will not commit. However, it does let Me know how important it is for him and I will use that to My advantage.

On another note, some subs don't want an O in session.