Come on folks - give the guy a break. So, he made a mistake but who amongst us have not at one time or another?
Money is not an issue so please feel free to recommend any tricks even if they are expensive!
Okay, if money is no object, then I strongly suggest that you get the three card monte DVD by School for Scoundrels or Daryl Does the Full Monte by Daryl.
Depending on what you want, specifically, one is better than the other (Daryl offers a massive amount of moves, Scoundrels offers a several strong routines and a full history of the game).
Once you get your DVD, sit down and learn how to do a pure three card monte without any gaffes at all. Put the time in and really learn it, forward and backward. While you're learning this, don't show any tricks to your friends, at all.
Now, once you've got it down perfectly, the next time that you're out with your friends, you can hand them a deck of cards, ask them to take out the cards that you'll be using (ace with two dueces for "chase the ace," two aces with a queen for "find the lady," etc.) and then they can examine those cards under a microscope if they want, because you'll be doing a fully ungaffed version of three card monte.
Or, if you think that won't be enough to prove your point, then ask one of your friends to purchase a deck on the way to the pub for which you'll pay him. Then, have your friends open the deck, get the cards and start from there.
A word to the wise, though:
Show your routine
before you start drinking.
Mike.