You know which card your spectator is thinking of and remove it before they reveal it!
How? Make sure you set up the cards so the 'Jack Of Hearts' is at the front facing your audience. Fan the cards and ask your spectator to think of a playing card in your fan of cards. Then mix them up and always remove the 'Jack Of Hearts' and place it in your pocket. Tell your spectator you have removed their selected card and you magically know what they are thinking! Their selected card upon fanning the cards again has vanished?
The secret move is when you place the 'Jack Of Hearts' in your pocket you reverse the rest of the cards end to end and the card suits/pips will be different. The cards are specially printed. No matter what card they choose - when you secretly rotate the cards during the trick and re-fan them they are always different. Furthermore if they have chosen the 'Jack Of Hearts' then it becomes amazing magic and you can then take it out of your pocket and show it. Never reveal the card in your pocket if they do not choose the 'Jack Of Hearts'.
Never repeat the trick to the same person twice!