This setting utilizes two SKUs for the named inventory item. They are two separate inventory items in the system which are tracked and updated as needed. One SKU is prefaced with a U to indicate the item is used, the other has no prefix to indicate that it is new.
For example
GBJ2 is a NEW Gameboy Joystick 2
UGBJ2 is a USED Gameboy Joystick 2
System Setup: Inventory: Trade-Ins (Used Items)
Procedure
1) create an invoice and choose the button Take Trade In
2) you are prompted for a Cash or Credit Payout method
3) you are then prompted an existing SKU number
4) enter GBJ2 information about the item's stock status and payout value will be displayed.
5) choose to Accept or reject the trade.
6) choose OK and the customer's invoice will show a payout value