The carrier interface charge varies, if the fare is $59 or higher it usually is $19. I purchased a $19 fare at Trenton once because I was already there. In that case the CIC was like $4 and I wouldn't have done it if I hadn't been,at the airport. They were really nice and they actually gave me a STRETCH seating upgrade for free (though I wouldn't expect that ;-) ) As far as them not issuing tickets at the airport if that is true they'd be in BIG trouble with the department of transportation because the reason that they can charge the fee is because there is a way to avoid, it by going to the airport. If there is no way to avoid it it would have to be included in the fare and the US Domestic Transportation Tax of 7.5% would apply to it and Frontier would owe alot of money, Its actually a bit shady that they charge a higher fee to add baggage at the airport because we know they do this to discourage purchasing at the airport.