Not true at all actually.
You CAN shut someone down in a nice manner. Think about it. Someone calls you on a double lift.
What do you say?
ANYTHING that you say is shutting them down, because you're not going to just say "yup, turned two."
So you must "prove them wrong" but do it so that you aren't really saying to them, "shut your mouth, stop talking, you're wrong, I'm right". You may ask them to show you, they decline nicely, and you continue.
You're just walking around saying everybody's opinion is garbage.
Is that so? How long have you known me? How many of my posts have you actually read? Why do you feel the need to support your "argument" with unsubstantiated personal criticism, for that matter? It doesn't say much for what you have to say.
I believe you're a little confused though. You can prove them wrong, and diffuse the situation, in a nice manner. Shutting someone down, on the other hand, by its very definition, is an aggressive action. For example: Performing a KM move diffuses the situation. You hand the card over. It's one card - easy. There is a huge difference between "shutting someone down" and "recovering". I'm not saying you can't recover from it. I am saying however that to challenge and potentially humiliate an audience member is irresponsible at best.
And that is all I'm arguing.
I don't say anything, really - because the problem is, they're right. I see no point in saying anything to challenge them. I find it inappropriate to challenge them verbally because really, you ****ed up, it's your fault. No need to take it out on the spectator.
Let's say you ask them to show you. What are you doing, exactly? You're challenging them. They cannot match. They feel inferior, perhaps embarrassed. You push them into a shell. Essentially, you cut someone down, and whether or not you say please is irrelevant. The essential action remains the same - you are increasing the rift between magician and audience. You make them look bad in front of their peers, perhaps even get a laugh at their expense. And why? Because you ****ed up.
Last time I checked, humiliating spectators because you screwed up isn't part of our job.