Chapter 11
A customer brings a shirt back.
You find the return by the receipt or invoice number the customer is holding — never by asking who they are, because a walk-in customer has no account to look up.
The system already knows exactly what was sold on that receipt and how much of it is still returnable, so you pick the lines being returned rather than re-entering what they bought. If the customer is exchanging rather than simply returning, the new items go on the same visit: paying more settles the difference, paying less refunds it, and an exact swap settles nothing further.
One receipt, and nothing is guessed
An exchange prints as one receipt for the whole visit — the returned goods as a negative line, the new goods as a positive one — so what the customer actually owes or is owed is the one number at the bottom, not two separate slips to reconcile by hand.
What can wait: you do not need to decide store policy questions — how many days, receipt required or not — inside this guide. Those are choices you make for your own shop; what the system guarantees is that once you have decided what to accept, entering it is exact rather than a guess.