FILE - In this Thursday, April 8, 2010 file photo, a Frontier Airlines jetliner arrives at Denver International Airport. Carriers are offering more deals to passengers who book flights directly on their websites. Frontier Airlines is the latest carrier to jump into the fight, announcing Wednesday, Sept. 12, 2012, that it will penalize passengers who don't book directly with the airline. (AP Photo/David Zalubowski, File)
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