To check a customer's transaction history, the first step is to open the Main Menu in the top-left corner of the screen
Locate and select the desired customer.
Next to "Personal Info", access the Sales tab.
That's it. You now have access to a customer's purchase history.
If needed, you can tap the trash can icon on the top right-hand side of the screen to cancel the transaction.
Or tap the sale to see detailed information.