While many flights are stuffed to the gills, there are still days and times when empty seats can be found. Typically, that is more likely on flights that rise before the sun, or on off-peak travel days such as Tuesdays and Wednesdays, says Joel Frey, a spokesman for Travelocity.com.
Gate agents tend to feel less pressured early in the day, says Lauren Sullivan, the North American site editor for CheapFlights.com. They may be more inclined to dole out upgrades if available.
DiScala always checks his flights 24 hours before departure to gauge how full they may be. If a flight is completely oversold and the airline is looking for volunteers to catch a later flight, that's a perfect time to negotiate for an upgrade, he says. Furthermore, a weather delay can work to your advantage if you're rebooked on another flight, and the only seats available are at the front of the plane.
And don't forget to play an emotional trump card. Let the airline workers know if you're celebrating a special event like your honeymoon, Sullivan says.