Duping is possible in any game that has items, it usually is complicated and 99.9% of times it's shared only with high ranked/respected persons in that games hacking. It's some kind of rule someone invented, and it's logic, cause if you share a dupe bug on a mmo with everyone, it will be patched in no time. Only elites know it and they will tell it only to other high trusted elites. I know it because there was, and still is on private servers, a dupe glitch on wow-wotlk. They patched it in cata because some genius went telling around. you know those "minor glitch fixes" they say, that's it. i'm going OT sorry, anyway there surely is a tf2 dupe glitch, but surely, it wont be shared.