What I find is that sometimes when a WG is giving you oral she might switch to a hand job and do it very quickly to try and get you to cum. If this happens to me I will always just gently hold her hand to slow down her action and if she doesn't slow down I'll ask her to stop. It's always my aim to cum just the once on a punt (even if more than one cumshot is on offer) - and I'll try to cum as near to the end of it as I can.
The worst experience I've had where a WG was just trying to make me cum was when I went to a massage parlour in Marylebone which I had booked for a 1 hour tantric massage. This would include a handjob at the end. When I got there and met my masseuse, after a few minutes of "treatment", she asked me after a few minutes whether I wanted "more service" and I told her I just wanted what I had booked. She seemed pretty pissed off and shortly after that proceeded to wank me furiously to try to make me cum. I held her hand, slowed it down, then gently moved it away from my cock. Then her other hand grabbed my cock and started wanking it, so I repeated my method of holding her hand gently, guiding it away from my cock. Guess what, her other hand went back in for cock action again. By this point it was becoming a bit like something out of a cartoon (albeit not one suitable for family viewing). After a couple of minutes of this she shouted at me, "WHAT!". This was 15 minutes into the 1 hour session. I actually managed to make the session last for another half an hour - 45 minutes in total. She was wanking me but I was trying really hard not to cum, concentrating on anything but sex - bacon sandwiches, what I'd seen on TV - anything but what was happening to me - and all this just to spite the girl who was trying to rip me off. After half an hour, the excruciating look of disgust, impatience, frustration and anger on the face of my "masseuse" became too much for me. At this point she was using both hands and going at it like a steam train. I was thinking that any minute now she's going to utilise the bow-drill method - like trying to start a fire with my cock. I came on her hands and that was the end of the session. Needless to say I never went back.