you have to take a very expensive item and put it in ur junk then go to a shop and go to junk then press Y then A almost at the same time so u should sell it twice even though it's one item then buy it back and repeate.(NOTE: this may take a few tries but once u get the hang of it it's preety easy.)
And to do it with tomes you need two of them. And this is very, very easy.
Basically to duplicate items, you put them in your junk section and then sell one to any vendor. It's easier if you haven't sold anything because their junk section is empty. Then, as the previous poster said, press Y, and then A *immediately* after, and you sell the item twice. I do it with my thumbs. And because you sold one already, the amount you just sold doubles and is added to the total.
So, if you have nine, you sell one, and then after you do the glitch, you have seventeen. Buy all but one back, do it again and you have thirty-three. Do it again and you have sixty-five. Here, you should buy only 34 back, and after you dupe them you should have ninety-nine, which is where you stop.
Then you buy ALL of the item back to do the glitch. And if you make the amount go over ninety-nine, if you try to buy the ninety-nine and the smaller number back, you'll only be able to buy the smaller number, ninety-nine just disappears. Or both do, and then you can't do the glitch anymore, so be careful.
To get two tomes to dupe, you should have around 80 gold, to be safe. Do the glitch with something like Injury kits or Lyrium potions. Then after you get to the party camp for the first time, buy both tomes from Bodahn. Go right back to Lothering, and then back to the party camp. Bodahn's inventory resets after you leave and come back. Which also means that anything you sold to him for storage will be gone. Anyway, buy the two tomes once again, and there you have your duping material.
Oh, and to make buying large amounts of stuff go faster, hold the stick right and and right on the d-pad.
I was so proud. http://www.gamefaqs.com/boards/genmessage.php?board=939933&topic=50189776
i'm pretty much just starting the game, so all this kinda sounds like a new language to me but when i put the game in there's an update...does the update void this money glitch or is it an earlier update?