Buy tickets on an airline that will refund the difference if a fare goes down

Let’s say you’ve done your best to find the lowest fare, and then the day after purchase your non-refundable fare goes down $100. Sure, if you ask for it you can get a refund for the difference, but it’s a little-known fact that some airlines will charge you a “service” or “administrative” fee as high as $100 for domestic fares or from $200-$300 on international ones, wiping out any savings. United, however, will give you the entire fare difference without extracting a fee, as will US Airways and JetBlue as long as you accept the reimbursement in the form of a voucher good for future travel. Northwest charges just $25, for both domestic and international fares. American and Delta extract the $100-$300 fees; Southwest gives you a credit for a future flight without charging a fee. Even on these less generous airlines, however, we’ve heard of plenty of instances where a polite entreaty will get you a full fare difference refund without the penalties, so it’s worth try.