I found a duplication exploit for this mod (I think? I never noticed this happening in vanilla Terraria, though I didn't really check, either). If you sell a stack of an item (I tested with souls of flight) to the Cobbler, you can left-click to buy 1 item from the stack, but you end up with a copy of the entire stack in hand. I did not check how much you end up spending by purchasing back just 1 item from the stack, nor did I check if this works with other NPCs.
example: sell 103 souls of flight to the cobbler, buy back 1 by left-clicking, there are now 102 souls of flight in the cobbler's list of items he's selling, but you have 103 souls of flight in hand. Place the 103 souls of flight in your inventory, then left-click to purchase another soul of flight, and there are now 101 souls of flight for sale, and after placing the souls you just bought in your inventory, you will have 205 in your inventory.
