Her ticket credit on United Airlines was worth about half what she expected — an increasingly common complaint among air travelers.

What are airline ticket credits really worth?

Bethany Tully might have been forgiven for her confusion. After canceling an upcoming flight from San Francisco to Boston under unhappy circumstances, she discovered that her ticket credit on United Airlines was worth about half what she expected — an increasingly common complaint among air travelers.

She tried to cancel bookings within 24 hours for a full refund, the airline would be happy to issue a ticket credit instead.

What is an airline credit really worth?

It happened to Louise Andrew twice last month. She made reservations on the United Airlines Web site, tried to cancel them within 24 hours for a full refund, and was told that the airline would be happy to issue a ticket credit instead.