 A person who paid full fare will have higher priority than someone who purchased a 21-day advance fare.Some low-cost carriers, Southwest Airlines in particular, have policies that only allow full fares to standby.This means that if one purchased a discounted airfare, like a web-only fare or 14-day advance ticket, they would be ineligible to fly standby unless they upgraded their ticket to a full-fare (unless the original Southwest Airlines flight is delayed, in which case no upgrade would be necessary).