If one of your Mobile Point of Sale users fraudulently uses the platform (gives away tickets, do not return the cash collected, etc.), the first step is to revoke his/her access to your events. Message ticket buyers to work out a resolution with them before canceling their orders as they may not be aware of the problem. Ultimately, you can cancel orders placed by fraudulent users from the "Orders" panel in your event dashboard on a case-by-case basis.