This card trick is one of the easiest to do but still it has a great power and influence in the audience.It is the first one I learned but I recomend it for all types of magicians.
There can be many ways to execute the trick but I will teach the one I’ve been doing since I started as a magician.
Tutorial
Step 1: Shuffle. It is totally an impromptu trick, you can let the spectator shuffle the cards.
Step 2: Grab the deck and look secretly at the bottom card, that will be your indicator card. Memorize it.
Step 3: Let the spectator pick a card randomly. Make sure to let know to the spectator that you are not seeing their card. (In the case that the spectator picks the bottom card, memorize the new bottom card).
Step 4: Place their card on top of the deck face down, without looking at it. Start doing cuts, but only one at a time, this way your indicator card will be placed on top of the spectator’s card. You can let the spectator make this cuts carefully and you can even make false cuts.
Step 5: When you finish making the cuts you want, start flipping cards one by one from the top and tell the public that the can just look but don’t say anything. When you flip your indicator card you will now know that the next card will be theirs but, if you want to win money, just take a glance of it and keep flipping cards.
Step 6: Now that you saw their card you can make the bet. You can say “I bet you 50 dollars if the next card I flip is yours” The most probable thing that can happen is that he/she accepts the bet because if he/she paid attention, their card has already passed and they will think that you are going to fail. Then just flip the already passed card and you won!