Trade in

This is used in the instance of a client items from you, however a trade in is involved, hence the client does not pay the full price and you receive items from this trade in which needs to be put into your stock.

Create a stock item for the item(s) you trade in.  On the Additional tab tick the box "Trade in/Empty"

The following will then occur on invoice.

Add items being sold to the customer, add the item the customer is trading in e.g. empty coke bottle.  The system will now deduct the trade in item amount from the item being purchased, and increase your trade in stock item with the amount being traded in.