This is what I would do. If there is a heckler trying to take over the show. Here are a few things you could do.
-Say "alright if you know soo much about this trick than you finish it". Then leave.
-Tell him or her "sorry, I didnt know you where a magician. You wont be interested in tricks you already know". Then leave.
-Just leave. Then the rest of the audience will be mad at the heckler for making you leave and the heckler will feel like an idiot.
-The heckler says"I know how thats done"! Then you say"Ohh cool, how?
-Or tell them "sorry, I didnt know you where a magician. Why dont you show some of your tricks"?
-" Sorry, you should have told me you werent interested in magic."
-Say"Ohh cool, your a magician? Can you teach me the______? Or the ________? Or the ______?" Then keep naming tricks and when they keep saying "well no" Then say " well your not a very good magician then". And leave.
-If the heckler keeps on saying stuff just ignor them and the rest of the audience will get annoyed and tell him or her to shut up. Or the heckler will realize that noone is listening and he will get tired of talking and will feel like noone cares and feel like an idiot.
Remember, you cant get the audience upset. If anything let the audience get mad at the heckler not you. Dont say these things in a mad way say them in a joking kind of way.
Hope these help you! cardkid.