Under the Full Fare Advertising Rule , airlines must display the full cost of an airline ticket, including taxes and mandatory fees. However, airlines may have additional fees for checked bags, seat assignments, and other items. These additional fees do not have to be displayed and reduce the tax that airlines have to pay. Travel agencies and online aggregation websites must display the base price. The Department of Transportation’s power to enact this rule comes from its statutory authority to prevent “unfair or deceptive practices.” The Airline Deregulation Act of 1978 exempts airlines from state and local consumer protection laws and many federal consumer laws, so DOT and FAA regulations in this field are incredibly important. All additional charges must be offered on an opt-in basis. The passenger must affirmatively select to add a service to their ticket. An opt-out system is considered an “unfair or deceptive practice.” Cancelling a Purchase Within 24 Hours Passengers benefit from the 24 hour rule when cancelling or holding a ticket. Airlines must either allow you to hold your ticket and fare for at least 24 hours or allow you to cancel, at no penalty, within 24 hours of purchase. The 24 hour rule only applies when you purchase the ticket more than one week before the flight.