Air miles credit cards
Credit: Frank van den Bergh / Getty Images

We've fallen prey ourselves to the lure of (supposedly) getting a free or greatly discounted trip just by charging stuff on a credit card. But as with most things involving credit cards and the airline industry – perhaps the most notorious hucksters around – things are rarely as they seem.

For starters, air miles cards typically have annual fees that can run as much as $125 or more, which substantially reduces any perceived discount you'd get on a ticket. They also pack higher-than-average interest rates, according to Bankrate. And with virtually every card on the market, you are almost always subject to blackout dates, off-peak travel times – both dates and hours – as well as artificially inflated seat prices (so you may only be able to use miles to pay the highest price for a given seat, even if it's advertised elsewhere for far less). Plus, depending on whether or not a specific airline is affiliated with your card, you may have restrictions on destinations if, say, it doesn't fly to the Bahamas. Finally, you're likely to get hit with taxes and fees for using your miles regardless, which today can account for a substantial cost of ticket prices – in our experience, as much as half the price for some destinations.

If the above hasn't dissuaded you, then consider this: Since air miles cards typically give you one air mile per dollar spent, how much is an air mile really worth? The answer varies widely, but it ranges from as little as half a penny to as much as just six cents. For those who travel a lot on a particular airline or have high-volume credit card use (for work reimbursement, for instance), some cards may still be a good idea, however. Check NerdWallet.com to keep tabs on the few cards that may be worthwhile.