Trade-Ins usually give a payout to a customer, but what if you have products which have been damaged which you want to sell as a used item?
For example, you may have a damaged lamp table. You can make it a used item so that when a customer wants to purchase a new one, you could offer them the used, slightly damaged item and allow them to make a choice.
Follow the steps outlined for making an invoice.
Use CTRL-T to enter products as used, linked to new items. The Value will be your actual cost of the item which you invested in it. This is normally the value you would payout to a customer.
Before processing the invoice press CTRL-D to trigger a Discount of 100% to reduce the payout to 0.00. The costs of the items are retained, but there is no longer any payout.