Tha acts have been variable but the problem is that some have been introducing "false" moves knowing P & T will spot them, (eg appear to do a deck swap or clumsy sleight of hand) and use their limited time for leading questions, so they can deny the trick was done that way preventing P & T from pursuing alternative options - ie they get one shot.
I'm not sure you understand the point of the show. You see, this is a show about getting exposure, and maybe even some extra exposure in Las Vegas. Fooling P&T is the only goal.