There is very little the airlines won't do these days to earn a buck, and one of their primary goals is trying to make you forget that there are other ways to book flights than on their websites. Conventional wisdom has in the past been on the side of the airlines. After all, the thinking goes, when it comes time to change or cancel your reservation, you want to be able to call the airline directly, don't you? Those scary third-party sites, well, good luck getting someone to pick up the phone!

Times have changed. We now live in an era where you get charged $20 by your airline for wanting to book a ticket with a real live person (Hello there, Virgin America!). It costs $20 and up to put a bag in the overhead bins, for goodness sake, when you fly Spirit. 

Look – we're all for airlines not collapsing – goodness knows enough competition has been killed off already. But, bottom line, these days you don't get all that many brownie points for dealing directly with your airline. As we've pointed out before, Delta is not going to tell you that your best price and/or schedule options will involve flying out on Delta and back on US Airways. But a third-party online travel agency will do so.  The lowest airfares carry heavy restrictions no matter who you buy them from, making a ticket booked on an airline's site as punishingly difficult or expensive to change or cancel as they would be purchased from some off-brand third party site you've never heard of. (And boy, are there a lot of those.)

Another perk of dealing with a travel agency (whether online or not) such as Expedia: if there's a major weather event or other glitch, you could be on hold with your airline for hours. Travel agencies tend to answer their phones faster, so you can get rebooked faster.

One of the tactics that airlines have been employing to prove just how nice and friendly they are is the low fare guarantee, which promises all sorts of things to people who find lower fares elsewhere, once booking travel on an airline's own site. Some even offer refunds for the fare difference, if you can prove that you overpaid. And while you might be tempted to think this is a great reason to book directly, not so fast – plenty of the third-party sites have guarantees of their own, and some of them are actually quite good. We checked out the online travel agencies to see what their policies were; the results in this handy chart.

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How useful are the airlines' low fare guarantees?

Airlines that refund the difference if the fare drops before you fly