Hecklers come in all sizes for sure. For me, I have had some issues with people spoiling a trick here and there. They see a load, or peek at a card prematurely or perhaps they know a little magic themselves and they spoil an ending. This happened during a performance with an Omni deck a little while ago with me. Someone hollered, "The deck's going to turn into glass" right before it did.
If the tough spectator is like this usually I can talk with them and say something along the lines of, "Are you a fan of magic? You seem like you have seen a lot." Then hopefully I can leave with a friend who has a mutual respect for magic.
Believe it or not, those who love magic the most can be the worst audiences imaginable. Magicians generally are terrible audiences. Yet it is those who love magic who will likely book you more than those who don't.
Also Chris Ramsey had some funny things to say about this subject.
Then there are those who want to mess you up or ruin the magic for everyone else. Chris has some ideas here but I have a different approach. When someone is making me frazzled I turn to self working magic.
I would never dream of doing a double lift for a heckler! Any secret move of any difficulty is probably bad, the one time that it could go wrong it will.
I have a small repertoire of incredibly fooling, self working magic. I usually will pull out one of these effects. (I'd rather not share the specific effects I use here. They are usually the same tricks I use to fool my buddies.) That way I'm confident that I wont mess anything up and that everyone will leave fooled. It helps if the trick can be repeated as well, just to quell any guesses at a method.
Another way I deal with tough spectators is to involve them in some way that makes them look good. It has to be a specific type of person for this to work. They become the magician while I perform Aaron Fisher's Search and Destroy or I instant stooge them and they read their girlfriend's mind. If they are a know it all, sometimes it helps if they see a bit of the secret.
The last way, if nerves are steady, is to perform some cardistry or gambling moves. I will sometimes turn to displays of actual skill and take a break from magic until they leave. I might stack a couple hands in poker and explain what I am doing as I do it. In this way, the performance is still interesting but there is no worry that the heckler will reveal a method and ruin the magic. I'm just showing some magic related skills that I have picked up.
Something like this would work:
This would also work: