He’s hustling completely untrained amateurs through darkened passages. He’d better make damn sure its completely safe. Unless its a preexisting condition, Copperfield/Copperfield’s insurer should assume full liability.
It’s not that difficult. Copperfield personalizes it; he gives them a signed autograph, “swears” them to secrecy. They’re now “part of the his show.” And, the real intent is just so that the 13 don’t start blabbing at the event itself and spoil a significant portion of the theatre’s audience.