My Airline Is Having a Sale, So Why Can't I Find a Deal?

— -- Each week, there's a steady stream of airline fare sales.

Some offer excellent deals, like the recent Oakland to Stockholm deal from Norwegian Air for just $159 one-way. Other sales are not quite as eye-popping but offer nice prices. Almost all also offer a ton of fine print.

If you read the fine print, your eyes may pop again. It includes a series of hurdles to jump through to get the deals that are advertised. Since most of us don't read the fine print, here's what to look for.

5 Things to Look for in Every Airline Sale

You have to follow the airline's "fare rules" to get their deals but not all airlines use the same playbook so rules can vary.

1. Book-by date

Many airfare sales come with expiration dates like "book by Nov. 5" but what if you follow that rule and still can't find a deal? You probably didn't notice the disclaimer most airlines add and here's the one American uses: "Seats are limited and sample prices may not be available on all flights."

Translation: No matter how long a sale is supposed to last, the inventory of sale seats is finite; when those seats are gone, the sale is over.

Tip: When you hear about deals, shop immediately. The book-by date is only a guide.

2. Advance purchase

Watch out: Some airline sales require an advance purchase of two weeks. Others, like Virgin America, sometimes require bookings be made 21-days before departure. A sale may seem perfect for that trip you want to take on Tuesday but if you fail to book early enough, you could be out of luck.

3. Travel dates

Most airline sales are valid for specific travel periods -- sometimes weeks, sometimes months. It will come as no surprise to you that such periods are often less popular times to fly, but watch for two other exclusions.

Blackout dates: Typically holiday travel periods. Seats for Thanksgiving, Christmas, New Year's and often spring break travel dates are almost never included in U.S. airline sales. Once in a while, you'll see special holiday "deals" but these are rarely real bargains.

Excluded days: You're looking for seats within a sale period, you're shopping early, you're avoiding blackout dates but still can't find a deal? You may be looking at the wrong days of the week. Fridays and Sundays are typically no-fly days per many sales mainly because airlines know we want to fly those days and will pay a little extra. Sales for peak summer travel can be even more exclusionary, limiting flights to Tuesdays and Wednesdays only. Even now, some airlines limit their best prices to Tuesdays, Wednesdays and Saturdays.

4. Refundability

Do not ding your credit card before asking yourself this question: Is it possible I might not be able to fly on these dates? Most sale tickets are non-refundable and the airlines mean business. If a life-or-death situation arises, you can always throw yourself on the mercy of the carrier but expect nothing. If you know there's something coming up that might make it difficult for you to travel, consider taking a pass on the sale or paying extra for a refundable ticket. Or fly Southwest, the only domestic carrier without a change fee.

5. Fees

Thanks to those irritating airline fees, the value of a sale seat is not always easy to figure out. Here's an example of why you must factor in the fees: Spirit has a round-trip flight (LA-NY) for $422 and the second-best deal is $442 on Southwest. No-brainer, right? Not so fast! If you'll be traveling with a carry-on or checked-bag, Southwest is actually the better bargain.*

*On a Los Angeles-New York flight, Spirit charges non-club members $35 each-way per carry-on and $30 each-way per first checked-bag. Both are free on Southwest.

The opinions expressed in this article are those of Rick Seaney and do not reflect those of ABC News.