What should I say If they are sure they know how the trick works, but it actually isnt that at all? For example, I did Bite-out coin for a kid and he said he saw the missing piece fly from the back of my head onto the coin. What should I say to prove them wrong?

For the bite out coin do a switch and hand them a real coin.

That is what I have always done.

Then their should be no problem, its their coin and if they can examine the coin which they could and see thier is nothing wrong with it, then their should be no prob..

I used the coin trick as an example, what I wanna know is what should I say if they think they have it, but they dont.

Then say they don't, let them belive what they want to belive. And if they still think they know how it is done, and if it is a card trick, say then you would be able to do it then, hand them the deck, and they would not be able to do it.

I like it when people "know" how it's done because they won't start badgering you for the real secret. If they come up with a theory like that a coin goes up your sleeve, when in fact it doesn't, you could try and prove them wrong by getting them to put their hands over your wrists, or putting rubber bands on your wrists. But that could lead them to discovering the real secret if you eliminate possibilities as to how it's done.

Sometimes I just tell people fake secrets or give "subtle" hints. For 'Floating Dollar Bill' I say, "Don't touch that. You discover the magnets." or some such nonsense.

I don't remember where I got this, so the quote isn't mine. It works pretty well though, just don't use it on the wrong person.

"You are probably right," you say, but then add, "but then again, I tell everybody they're right."

It works well because if you tell them that they're wrong, then they use process of elimination, or just keep bothering you.

Sorry, I had to correct that !!! lol

I always tell them it is the smoke and mirrors! It is good for a laugh, and they get the point I am not going to tell them.

Well, this stuff always happen. Too common around the human race, haha the only way i do this is just say "maybe, maybe not".

You aren't out to prove anything to anyone. You are out to entertain. So tell them it is a magic coin, do your shuttle pass, and hand it to them to see for themselves.

Don't get them to do it themselves. Then they get to make fools of themselves with the benefit of props. They might drop the entire deck over the ground, and then they (and you) get to play a fun game of 52 pickup. Just let it be. That's how I do it. If they think they outsmarted you, that might just be how they enjoy themselves. Remember, the point is to entertain, not to always be supreme king (or queen) of everything.

I've always found that it's best to stay unconfrontational. If you say "well, you try", then, who knows, maybe they'll be right. It's best if you say something to the effect of, "no", but in a more creative manner.

I hand them a "clean" prop and ask them to show me what they think I'm doing.

I have one annoying kid in my school. He always tells that he knows how its done. One time i got very tired of him , and gave him the deck , so he can show me how am i doing it. I was performing invisible deck , but i switched it for normal. So he turned around and picked one card and turned it over. Then he asked me to name any card. So i names King of Hearts. So he spread the cards and it was 2 Of Clubs. He throwed the deck at me and ran away. So from now on he doesnt say that he knows how its done.