It wasn't hard, was it? Luring gullible idiots. Trapping them. Barty smiled politely at Tala before she departed, leading the man ahead of him and the hat-woman down a side alley. He continued talking to her about the book, by way of distraction, until just before Tala disapparated with a surprising, but telltale pop!
The woman's hand was nearly to her mouth - she was startled! - when Barty grabbed it and blackness squeezed around them before anything else could happen. When it finally dissipated, Barty blinked a moment, bringing in the room around him before whipping out his wand. He saw the man lying petrified on the floor.
All right then. Aiming his wand at the stunned woman, he called out: "Petrificus Totalus!" And she was down for the count, blinking wildly, immobile on the stone floor. The Ravenclaw smiled, turning his eyes to Tala. "Well!" He wiped a hand across his brow in show.