The following example:
Well, you should have thought of as the NPC paid poco huh!
But here comes the secret, we note that the durability of the item is 37/117!
So let the anvil of the Dean, or any other NPC arrange items, click it and click Fix
When you open the inventory, click the item and click fix, you will pay from 1 to 15k, depending on the durability of this!
After fix, let's see how the NPC will pay.
Look, the price nearly quadrupled!
Selling swords, the price can go up 6 times!
PS: Sorry if there is any error in Topic English, Google Translate is not perfect.