Airlines can let passengers hold a reservation at the quoted price for 24 hours before paying, as American Airlines does, or let them cancel without penalty for 24 hours, as most other carriers do. Some experienced fliers suggest that you buy two one-way tickets if you can replace either one for less than the change fee on a round-trip ticket. Goldstein says you should book ahead of time because fares do rise closer to the flight, "but wait until you are as confident as possible that you're actually going to make the trip." [...] You hope and pray your flight is severely delayed or canceled," Hobica says, because you are entitled to a refund if the airline can't honor your ticket. A start-up called Flyr lets you lock in a fare for up to seven days for a fee of $5 to $35 depending on the flight without buying the ticket, says the firm's product manager, Andrew Jing. There are limits to its service — American Airlines doesn't allow its fares to be displayed on Flyr or a similar service offered on Hipmunk. U.S.