The exact size the student wants is not available — only one size larger or smaller. The student must decide what to do.
The card machine is "broken," and the store only accepts cash right now. The student has to react and solve the problem.
The price at checkout is different (higher) than the tag said. The student has to politely question it.
The exact item the student wants isn't available, but the assistant suggests a similar item in a different color/style. The student must decide and respond.