Bring in many sales at once from an Excel sheet. Each row is one line of a sale; rows with the same invoice number become one sale. Customers are matched by phone number first, then by name, and you check every customer before anything is saved.
Blue columns must be filled on every row. Leave Invoice_No blank and each sale is numbered for you, the same way New Sale numbers it. Write the customer's phone number in Customer_Phone — it is the surest way to find the right customer, even when two customers share a name. Leave the customer blank, or write cash, for a walk-in sale. Write General in Bill_Group to give every customer that invoice (dues, a monthly fee), or a customer group's name to give it only to that group.