I found some great information about known scams in World of Warcraft on wow.stratics.com:

No matter what game it is, this same exact scam happens in every single game around:  Some people have even tricked others into letting them kill them for the dupe to work!

Duping is the ability to clone an item illegally. We understand that the temptation is enough to drive one crazy. A grief player (a player who wishes to cause grief among other players) will tell you to give them one of your best items so they can “dupe” it. When this happens, they either log off, kill you, or run away, and you’ll never get your item back, not even by appealing to the GM’s!

If someone wants to dupe something for you, just say no. World of Warcraft looks to be an extremely dynamic game. By that, we mean that if a duping bug does occur, the World of Warcraft Live Team will fix it within a few days of its discovery. Keep in mind that being involved in a duping exploit/scam, even if not directly doing the actual duping, might be grounds for immediate and permanent banning from all Blizzard games. This is a scam/exploit to avoid at all costs if you care about your account.