I just had this 'experience" with CO. I will get a "Travel Voucher" if I take my tickets to the airport (or ticket office).

CO put my flight in April on sale (again) for about $55 less than the previous sale price. When I phoned to inquire, I was told that I would get the "differance" ONLY if seat were available at the NEW sale price on the SAME flights that I had booked. I could NOT change anything (days, routing or times). Seats were available and so they will give me the differance in a voucher.

My neighbor next door, who bought tickets at the same time (he is staying a few days longer and has a different return date) could NOT get the 'differance" because one of his flights would "sold out" for the new sale.

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"Free" without charge or cost, having no obligation.