I don't know if the people putting in duplicates are doing it intentionally or not. When you get a round Robin with 100 cards in it it gets hard to keep from accidentially putting in a duplicate. If one person is always the culprit then, yes, ban him from future RR's. But keep in mind how close some of these card variations are and the sheer volume of the RR. I don't think duplicates should be allowed since I recieved a RR recently where two duplicates were allowed. Even though the RR stared with 60 chips, it seems like everyone took two different chips and left two duplicates. Net effect was there were 30 chips in the RR instead of 60.