In the book Session, the magic of Joel GIvens By: Joshua Jay, there is a fantastic trick called heckler stopper. The heckler shuffles the deck after picking a card. YOu then show he shuffled it back an face. You fix it, produce their card which the audience saw, but they argue with you saying it was a different card, and you produce that from your pocket saying you don't have it in the deck.
This can really insult a heckler and make the m feel terrible so only if you feel you need to.
Definitely check out this book though, Excellent stuff.