No fee if you buy at the airport? Who does that?

Q. I'm flying from San Diego to Las Vegas on Spirit Airlines and noticed that they charge $18 per ticket to use their website for booking flights, but it appears that you can buy the ticket at the airport and avoid the fee? This seems counter-intuitive. How many people actually bother to drive to the airport to buy the ticket?

A. Probably not many. After all, it's a hassle and you'll probably end up paying a parking fee. Spirit knows this. However, since some Spirit fares are actually $18 round-trip plus tax, the online booking fee ends up doubling the price of the fare. I suppose if you're buying multiple tickets or traveling with a group, then it's worthwhile to buy at the airport.