Anything that might go wrong, will go wrong at the POS, and in real business environment, flexibility , user friendliness, features / functions, automation, speed and accuracy are factors to be considered.

The more advanced SOP (Standard Operating Procedures) below is meant for chief cashier, or branch managers:

No	Scenario	Common Mistakes / Case Study	Preferred Procedure	Remarks
1	Customer bought something, come back to exchange the product with something else.	Method 1: The cashier simply issue additional cashsales, without collecting the full amount (cash or card), resulting in wrong figures in the cashier collection report. Method 2: Use the "Cancel Cashsale / Invoice" function.	Procedure 1: Condition: Exchange happen the same day Procedure 2: (preferred) Use Sales Return	Also see: 1) How to choose Sales Return Options?
2	The cashier wrongly key in the item code, and the invoice or cashsale has been printed.	Method 1: Cashier perform a sales return on the cashsale and invoice.	Procedure 1: Use the "Cancel Cashsale / Invoice" function.
3	The cashier entered the wrong price by mistake when issuing Cashsale and Invoice.	Method 1: Cashier perform a sales return only.	Procedure 1: Use the "Cancel Cashsale / Invoice" function.
4	The cashier entered the wrong salesman information when issuing the cashsale or invoice.	Method 1: The cashier simply cancel and re-issue the cashsale, messing up the sales reports.	Procedure 1: Use the "Cancel Cashsale / Invoice" function.
5	What if the item that we are selling to the customers does not exist in the inventory? Or the system quantity is already ZERO.	Method 1:
6	The cashier choose the wrong credit card payment mode.
7	Customer bought products from branch A, and exchange it with a different product in branch B.
8	Cashier entered the product code, product price, and everything else correctly, except for one or few of the product serial number.	Method 1: The cashier perform sales return, or cancel cashsale / invoice.	Procedure 1: Use the Edit Invoice function to swap the serial number.
9	Service and Repair (non inventory items).		Procedure 1: Refer to the following for more detailed explanation: a) Services and labour b) Third party services and labour