I've been using this for quite some time now, decided I'd share it with you now that Stargate75 caught me and permabanned me for it.
Step 1: Put all the items you wanna dupe into your main character, make sure he is the best character you have!
Step 2: Put a big backpack on your second best character, make sure it's big enough to carry everything you want to dupe.
Step 3: Log into Outlands with your main character, then log out and do the same for your second best.
Step 4: Change the clothes of both these characters then delete them.
Step 5: Make 2 new characters and make use the same name and clothes as the ones you just deleted. They will have the exact same stats and inventory as your characters before you deleted them. BUT your other character that was supposed to have an empty backpack will now have the exact same gear that you put on your main.
You have now successfully duped, enjoy your items!