Here's a short article on how to shop for good air fares -- by people who help to set the fares...
1. Book early-ish. Hardly an exact metric, Brunger concedes, but it means not waiting too long, hoping that an airline will have too many empty seats on the flight you want three to four weeks before departure and get desperate to sell them. (That’s exceedingly rare, and means something went wrong for the revenue manager.) The closer you get to the advance-purchase deadlines, the more clarity airlines usually have on their pricing forecasts. When it works as planned, revenue management means an airline has sold exactly the number of seats at each fare level that it had intended—closer to departure, the seats that are left cost far more.
2. Book at a price satisfactory to you. If you can live with the cost and it seems decent, take the plunge. “If the fare feels like a fairly good fare, I would buy,” Nason said.
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