Duping isnt hard to a certain extent..this is the method i used to dupe.
*Note Dont use an authenticator or have one attached
Threw all my best items and all my gold onto 1 account and kept them there for a week...Gave my IRL friend my pw and account and had him xfer it all to his account from his place incase they did an ip trace. If you want you can have him change your pw and stuff to make it look like you really got hacked too.
Once it all has been transferred, log on your account and pretend like you got hacked/jacked. Submit a ticket for hacked account and request a rollback.
When i did this they didnt question me much or anything at all..they just wanted me to confirm that i wanted a rollback and asked approximately when i think i got hacked and i gave them a date.
1 day later my account was rolled back and i got all my gold and items back. I thought the items on my friends account would poof or it would poof if they clashed with my new set but NOPE..i got em all back onto my account..played for a while and they all stayed with me as well as my gold.
If you wanna dupe more..just file another claim as each account has 2 rollbacks. Once that account is done..just move on down the line and keep doubling up.
*Note I only did this once and this was done about 3weeks ago so i dont know if they changed anything as of today.
I only did this to test if i could double my gold/items and I DID.
Im gonna use my last rollback once i get about 100mil gold and a few more godly items since this account will no longer be able to use RMAH after 2 rollbacks/compromised.