Oh, clever idea, but probably wouldn't work. First off, it's labor intensive (you have to go to the airport and check in, it's not like you can speculatively buy 500 tickets), and the amount you could potentially make is bound not only by the ticket price but by the fact that you can probably only reliably make a profit during rush times (i.e., Thanksgiving, December). Also, if you guess wrong and a popular flight did not fill up -- you have to take the flights!