I was performing Two card monte from Born to perform, and the little S O B after turned the cards over before the trick was over! I just pretended that it was suppose to go that way. Any other sugesstions?

Well, I put the deck on a window sill or a table and hold their wrist so they cant turn their hand over. Or, you could get a toy gun and point it at them the entire trick.

Make it very clear that it is a memory test and don't turn it over or its cheating. If they still turn it over, don't perform for him/her.

Exactly. They are no longer worthy of your performance.

A few people have fallen into that category for me.

very well but this has happened to my friend PLEANTY of times

I get that alot. just not on thta trick. forget the name. penguin doesn't carry it, but I say if he flips it, just slap the SOB and walk off...

Jeesh, you guys are violent. Ussually when they turn it over the card in their hand is already changed, then I hand them the other changed card. It almost never happens to me though as long as you explain it very clearly.

If you can give a reason as to why they can't turn the card over, typically they won't. It's only in situations where there is no reason, or you just say "Don't look at them", that they'll want to sneak a peak.

I don't do the Two-Card Monte until I have done a couple tricks where it really doesn't matter if they turn the card over before I say so. I then notice if they keep doing it repeatedly, and if they do, I don't perform the TCM for them. I know you'll probably be thinking..... "But it is an awesome trick! How can I just not perform it?". Well save it for another day, on someone who will enjoy it. This is especially true if you have an audience, because it don't matter how good the trick is, if he busts it, he busts it.
If you can't think of any to do, start to perform the TCM, when you hand him the Ace, just watch how much he checks it while your talking. If you notice he keeps looking, witchout skipping a beat, take the ace back and perform another trick. It may confuse people a little bit with all the patter that now is gone to waste, but a true performer can improv his way out of it and into the next trick.
It has been my experience, (and there really isn't a whole lot) that the hardest thing to learn in magic isn't the sleights, or the patter. It is learning when NOT to do tricks for certain people. It takes a bit of learning each persons psychology and figuring out what trick will get the greatest reaction.
Hopefully this helps.
Hopefully this helps.

If they turn the cars over when one has changed, and one hasn't, pretend that that was supposed to happen. One of the cards changed. Amazing! Continue the trick, and then, both cards will have changed. It's a virus! It takes some thunder out of the final revalation, but it works.

That should not be an issue. It's called audience control. You all will learn it with experience.

Just make sure you explain everthing as clear as possible, and if a person is not doing the things they are supose to, then just stop doing it for that person.

I assume you're talking about "Honestly, Which is it?":

I tell them if they'd like to play a game. I give them the first card and show mine. I ask what card are you holding and look at them like I already have done something sneaky. They will either say "Queen of Hearts" or they will mistrust me and look at it.
If they just say "Queen of Hearts" I'll say "are you sure? *give them a real cocky smile* Take a look at it, go ahead. See? Nothing funny." The people that only turn it over when you ask them to are usually the ones who will follow your instructions.

Different personality type:

If I ask them what card they're holding before the first switch and they flip the card over to make certian the cards is still the Queen of Hearts, I flip out. "DON'T LOOK AT IT! This is a game! *in a forgiving voice* all right, that was your freebie. But NO MORE PEEKING! *under my breath* cheater..."

Usually that little excersise will tell me how much contol I'm going to need to complete the trick.

As Wayno said it's all about spectador managment.

Make sure you 've mastered your sleights, as I have a feeling that your sleight of hnad looks suspiccious and spectadors don't trust you. If they did, then why would they want to turn the cards over?

Make sure that when you give them the secont card and then take the other card from their hand, as you go to turn over the card that you just took from there hand to show it, while showing it have it on top of the face down card in their hand. That way they can't turn the card over in their hand as you have the other card on top of it.

Then when you are going to do your *** change you must do it in a split secont and the EMIDIATLY place the card back into tehir hand right next to your other hand. Make sure you are talking to them when doing the change and never look at your hands when doing it. Look at THEM.

With experience you 'll learn how to control them.