Deceptive, powerful, hands-off effects that are easy to do.
“The Psychomatic Deck” by Liam Montier can be spread, mixed, and then cracked open to peek at a card. They can then shuffle it again and pop it in back in the box.
Everything is so fair that they’ll never suspect you just forced a card on them. Especially when you consider how, with proper audience management, you can have them do it all while you’re across the stage or street, or even in another room.