wong yu liang / Shutterstock.com
Editor’s Note: This story originally appeared on Living on the Cheap. When Carolyn DiDonato booked her ticket from Trenton, New Jersey, to Fort Myers, Florida, she says she was hit with a hidden airline fee. On the last screen, concealed behind a drop-down menu, Frontier Airlines revealed that she would have to pay a nonrefundable $23 carrier interface charge for buying her ticket online.