It's very easy and means by lvl 4 you'd have all 5 bag slots. Best done in Windowed mode. *On official server*
1. Buy an item from a player/npc * equipped the item before moving on, dunno if this is required*
2. Hold down Cntrl+Alt+Del and end the rfonline process. DONT EXIT THE
NORMAL WAY OR YOUR DATA PROPERLY SAVES!
3. Relog back in, bam you have your original item and its duped one. Both work and are droppable and are authentic.
TOO ******* EASY to dupe >_> That's the oldest exploit in any MMO.
Of course you can experiment with this method and try to expand its technique for better results.