The Effect:
An envelope is placed on the table, before the magic begins. With help from a number of spectators, a single card is agreed upon by everyone as their selected card. The envelope is opened and a single card dumped out to your waiting hand. One card, one selection, only one chance to get it right!

Absolutely no sleight of hand required... but it uses a common gaff available from any magic shop and a magic principle that's easy to master. It will make your spectators think you are a true magician!