How can a supervisor check the balance of a shop card?

A supervisor can check the balance of a shop card by swiping the card because this method processes the card directly through the electronic systems in place, providing immediate access to the card's information. Swiping the card connects to the database that holds the account details, allowing the supervisor to verify the balance quickly and efficiently. This method is user-friendly and minimizes the chance of human error that could occur with manual entries.

In contrast, entering the shop card number manually could lead to input errors, which may provide inaccurate balance information. Scanning an item associated with the card would not yield the balance of the card itself but rather information about the product. Logging into the point of sale system might provide access to various functionalities, but it does not guarantee a straightforward or direct way to check the balance of a specific shop card without additional steps or information. Thus, swiping the card is the most immediate and reliable method for obtaining the balance.