I need to be able to put a negative quantity on an invoice in books and inventory. Example, customer is buying part A, which has a removeable part, part B. Customer wants Part C which replaces Part B. We swap them for the customer. On an invoice we should be able to list part A, Part B as a negative(adding it back to inventory) and part C. Why should we have to go through an added step of a credit note? While the customer is standing at the sales counter? Added steps for employees creates room for more issues and mistakes, rather then a simple 1 step process. Please add this feature. It is a feature we miss from Quickbooks, which did this function without a problem.