While I am not sure I fully understand why that has to be a part of the contract and haven't looked up Nevada Commission rules, I was told the same thing at Harrahs, where I usually stay--and then the cashier traded my duplicate for another that she had in a tray in front of her--I tipped her a buck. I supposed I aided and abetted some awful criminal act but, heh, if roulette thieves can do their thing, I oughta be able to trade an SS or two.