why not just add the bounty system? players can put bounty on players and win the bounty in the arena. If a thief steal and is pointed out by the persons stealing from. For a
Bounty command.
Apply a bounty on him a cap of 5000 gold pieces and a low of 100 gold pieces. (This is just an exmaple) Or just make it able to bounty people period, you pay double to put a bounty on someone head. Put a flag (bounty) next to the name. stealing can be tweak for a auto bounty and double for the person that does it more then one time.