In the book, Cam Jansen and the ghostly mystery Cam and Eric [her friend] are on line to buy tickets to a concert performed by the Triceratops Pops when somebody in a ghost costume starts scaring people by shouting”BOO!”
Then, the ghost scares an old man and it nearly makes him have a heart attack, and while that was happening the woman selling tickets, Sally, realizes that she’s been robbed. She said that the ghost threatened her to give her all the money that she had from selling the tickets and then give her all of her money while the ghost pointed a gun at her head.