This is how to normally dupe.
1. Make this a macro
Code:
/script local function buy (n,q) for i=1,100 do if n==GetMerchantItemInfo(i) then BuyMerchantItem(i,q) end end end buy ("Red Ribboned Wrapping Paper",249);
2. Buy a single Red Ribboned wrapping paper from the general vendor.
3. Use the macro to buy 249 red ribboned wrapping papers.
4. Wrap your item with the single wrapping paper.
5. Move your wrapped item into the slot with 249.
6. Unwrap the stack of 240.
7. There is now 240 of the item that you wrapped.