Once you get good enough, your only reaction will be "It's because he/she is magic."
I usually don't perform a trick until its been perfectly practiced to death.
Whether you know the trick inside and out or just learned it, you're going to run into these people. It doesnt matter how well you performed. Usually they are drunk or just full of themselves. My take has always been to say, "oh yeah??... indulge us... the stage is yours..." Then they try and can't and offer up some sort of speculation as to how you did it, and whether it's right or wrong, now it's your time to be the heckler.... I've rarely been in this situation, but when I have, I let them make fools of themselves and then stop them and say...."Ok...That's enough. I never claimed to perform miracles. I'm a magician... an artist of illusion... This is what separates you and I. I make this look good and you do not. Thank you for the comedy part of my show. Next time apply for the opening act and you might get paid. Now. Please take you seat." If I'm doing street magic and encounter the same situation, usually they are drunk... Then you speak "child talk" to them and agree that they know how everything is done and say something along the lines of let's keep it between you and I. After reading your post, please dont tell me you go out there and tell everyone that you are a miracle worker or the next messiah. That's such a lame way to present yourself. Present yourself as an artist. You'll gain a ton more respect that way.