I like your competitiveness and it's a desirable quality. I can see how someone would become very defensive when a question is asked of them. If they get upset with it, it's something for them to deal with. From my point of view, it is not attacking his ability, but it's expressing my belief that I saw/felt the ball land differently than he did. Do I expect him to reverse the call? No, it rarely happens and I don't expect it. It's for influencing the behavior going forward. (even though I recall one instance when my opponent reversed the call after searching for mark on a clay court - the ball hit flush on the tape and he called it out. When I asked if he was sure, he started looking for the mark and of course there was none. It was swinging volley from NML , there is no way it would not leave a mark) . The primary intention here is to convey that I see his bluff. It works many times - I have seen people double fault after a bad call. TBH, I have double faulted when I was still thinking about a previous call which I may not have gotten right. Now I offer to change the point, if I'm still thinking about the close call when I get ready for the next serve - it clears up the mind. And I agree with you that some may not like it when I question. I had a guy who retorted - ' Do you think I'm stealing a point from you?' I walked up to the net and said, 'no, I don't think you are stealing anything. But the ball looked very close to me, are you sure the ball was out?". I'm not expecting him to reverse the call, but I want to express how I felt and want him to know for the reasons I explained earlier. To summarize, IMO asking the question is constructive most of the time - to use tennis analogy, it's a high percentage play.