This glitch allows you to duplicate gear, ingredients, potions, and other stuff. 
First, you need at least two of the item you want to duplicate. The glitch is 
basically the same as the "Easy gold" glitch. Thus, it is best to only have the 
items you want to duplicate in both your and the merchant's "Junk" inventory. 
This help speeds up and organize things. Put at least two of the item you want 
to copy in the "Junk" section of your bag. Go to any merchant, and press Y to 
sell all the junk in your bag. Then, select the item from the merchant's side, 
and buy back all but one of the item. Next, select it when it is in your 
inventory again. Press Triangle followed by X very quickly. This requires 
precise timing like the "Easy gold" glitch and may require a few attempts, but 
it becomes easy to do after a few tries. You can keep repeating the process 
until you have 99 of the item. Some items will show in the merchant's inventory 
as being one row of 99, and another row of a different number (for example, 33). 
Sometimes the extra items can be taken and kept; however, other times they will 
vanish from your inventory. Be careful about taking the correct row. If you have 
the "Warden's Keep" downloadable content, you can store unlimited items in the 
bottomless chest so you will always have more if you ever run out and do not 
want to keep using this glitch. This glitch should also work with books that add 
Skill or Talent points. When you get any of those books, wait until you have two 
of them so you can make unlimited copies and max out your characters.