Sometimes, always, not always, never
Like anything, you will recieve multiple answers. For advertizing, one may say Always, becuase it seems thats what the gentleman are looking for, a responsive lady.
Being responsive doesn't mean you have to get off. I will admit, not all the time. Even if I really wanted to, my body my not be up for it, and wont allow me to. (different time in moon cycle, exhaughsted as you've been trying for hours)
But the one that will really make it difficult is if a gentleman keeps saying, "cum, cum, cum" if my body doesn't want to, I cant and your just making it worse. If you feel she will not be able to cum for you, just brush it aside, and continue on with other playful acts. Unless that's all your looking for is a lady to have an orgasm, then find one that promotes her responsiveness.
Not all gentleman cum their first encounter, or maybe its just me.
I guess YMMV plays into this a lot.
Good luck and be good, if you cant be good be safe.