"Psychic" is a mentalism trick that you can use in every situation. This effect proves that all is already written. Be sure that the fortune teller say the truth!
Take a deck of cards and a little book with a fortune teller on the cover. You take the cards out of the deck to show a normal deck. Ask a spectator to cut the deck. When it's done, ask him to take the 4 cards on the cut deck.
Why 4 cards?
You show the book and the 4 cards face down on the table of the fortune teller. Explain that when you met her, she made you cut the cut and take 4 cards too. Like the spectator did (Show again that the cards are different).
Ask the spectator to turn the first card in front of him on the table. Open the book and start to open the pages (slowly one by one). The card of the fortune teller is the same than the one he chose! Ask him to turn face up his second card. It matches too! And remember, the spectator cut the deck himself!
The third card is turned face up too and matches the book as the fourth card. Unbelievable! The 4th card matches!
Explain that the fortune teller asked you to choose one of the 4 cards that are on the table. Ask the spectator to choose only one card, the cards he likes. It's a totally free choice!
Let's suppose he chooses the King of Diamonds.
Show the book to the spectator and the crystal ball on it. Show that when you turn the pages very fast, there is smoke in the crystal ball, and then a card appears, face down... and the cards is now face up and it's ... the King of Diamonds!