To be honest, we wanted the approve / deny mechanic to be much more developed. Like paper's please, or like your game. As it stands, you just have to look for shoplifters and approve or deny as you like. As you discovered, it's a good way to get rid of angry customers. Or you can use it earlier and prevent customers from getting angry. Approve or Deny is just for feels right now. I feel bad when I accidentally approve a shoplifter. But there's no in-game penalty, because "Nothing can go wrong." We're working on an updated version with more extensive "papers please" mechanics on the customer end.