When a customer is returning goods to you, you can generate a new sales credit making the quantity negative which in turn affects the overall value and makes it a negative value.

If you have set up a rebate product, you can use it to enter a sales credit through the Sale Shipments screen.

In the Navigation panel, open Sales then click on Shipments.
Click on button New
Click in the Customer field and select the customer from the list. If the customer does not exist in Readysell, you can click Create Customer to create them.
In the Customer Order field, enter the customer's order reference.
In the Lines tab, enter the rebate as follows:
1. Click on button New
2. In the Product column, search for and select the product.
3. Make the quantity be a negative quantity (a minus - quantity e.g. -2 if returning/claiming for 2 items)
4. Make any necessary changes to pricing and discount information. The negative value of the pricing is determined by the quantity column.
Click on the Line Notes tab to enter notes/reasons for the credit.
Click on button Complete.
The Sale Invoice window displays.
Click on button Show in Report, then select the Adjustment Notes layout. The sales credit will display in a report window. From here you can print or email it.

Use the Send Print, Send Email function at the top ribbon to output it faster to printer or email without previewing the adjustment note to screen. You cannot pick and choose which layout you use when using this process.

If you are using the Credit action button from within a shipment and the sales order does not have a status of POSTED then you can decide as to whether the products you are crediting you require them to go back to allocated on the linked sales order.
refer to the link on system reference under 'Sale-Credit-Prompt-Qty-Reallocate':

Sales System Type

Browser not supported