Cleveland — We've all received a gift card - perhaps for a store where we don't shop, or just a card we can't use.

Some head to sites where you can sell those cards, which is a great way to get extra cash. And since some of those sites re-sell the cards at a discount, you can score some great deals.

But the exchanges aren’t a dollar-for-dollar system. What you can sell a card for is rarely the same as what you can buy one for.

Take iTunes for instance.

As Jill Gonzalez from the finance site WalletHub explains, “Because there are so many of those cards out there, we're not seeing a huge resale value. For a $100 gift card you'll probably only get about $72 bucks for it."

Wallet Hub scored 50 of the most popular gift cards and showed what you might get by selling one and the average cost of purchasing one on these sites.

For an example, let's say you got a $100 gift card for Kohl's, which is ranked 27th in popularity. And a friend got one from Disney, which is ranked 17th.

Wallet Hub calculates your friend could sell that Disney card for $78.91. That’s only a few dollars more than the $75.31 you'd get for the Kohl’s, even though the Disney card is more popular.

That's because the "resale" value on the Kohl's card is higher.

That Kohl's card will resell for about $96.30. The Disney card would resell for only $81.03.

Trae Bodge from Gift Card Granny, which sells discounted cards says, "It really depends on supply and demand when buying and selling discounted or unwanted cards. It’s really good to shop around compare rates and make your choice based on that.”

Regardless, it's still extra cash in your pocket.

And think about this. If you bought, let's say, a $100 gift card to H&M on one of these exchanges, it would only run you about $81.98.

Gonzalez says, then you can "Spend the full amount in-store as you would, giving yourself kind of a home-made discount.”

You can also use a card you bought for a discount, as a gift for someone else, and come off like a big spender.

Wallet Hub useful links:

Gift Card Ratings

Best Gift Card Exchanges

Gift Card Granny