what if

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I would like to know the meaning of "what if you had been the Queen?" in the next passage.

A man was having dinner with his parents at a stylish London restaurant. The food was superb, and the setting, complete with chandeliers, crystal and silver was unbelievably elegant. Nonetheless, when his mother's main course arrived, she felt the need for a little salt. Trying the three silver shakers that were on the table, she discovered each contained pepper. She called the waiter over only to be told that she must be mistaken. Each table always contained two dispensers of pepper and one of salt. A second attempt, however, showed that their table did, indeed, have three peppershakers. Horrified, the waiter immediately brought her a saltshaker. When it was time for dessert, the manager appeared, insisting that because of the oversight they choose something "on the house." woman protested, "It's not that important. "But, Madame," he replied in all seriousness, "what if you had been the Queen?"