Is there a way to squeeze even more out of pre-owned gift cards?

Yes, by pairing them with store sales and print-out coupons or online coupon codes. Secondhand gift cards are a growing market and are available from sites including PlasticJungle.com, GiftCardsAgain.com and even eBay (EBAY) . Discounts can be as high as 30%, depending on the popularity of the store. But if you stack them on top of other deals a retailer may be offering, you get an extra layer of savings.

A few caveats: Before buying a used card, check that the selling site verifies and guarantees card balances, says Steve Sultanoff, an adjunct professor of psychology at Pepperdine University in Malibu, Calif. (He regularly buys gift cards at a discount to cover his regular expenses, including 20% off Albertson s cards for groceries and 5% off Wal-Mart cards.) In some cases, retailer maintenance fees may have eaten into cards. In a worst case scenario, you could be victim of a scam. Individuals on Craigslist or eBay may keep a copy of the gift card s serial number and use it before you have a chance to do so. Others sell cards purchased with a stolen credit card, which all get deactivated once the issuer catches wind, says Sultanoff.

There have been problems in the past from auction and classified ad sites where there is no way to verify the balance or even the legitimacy of the card. Sites such as PlasticJungle.com say they solve that problem with guarantees that offer a replacement card or refund if the card has a balance lower than listed at purchase, or if the merchant will not accept the card. Although some merchant policies say gift cards cannot be resold or transferred, that s rarely a problem for consumers redeeming ones bought secondhand, says Steve Gill, a professor of accounting at San Diego State University. The point of purchasing a card is, after all, to give it to someone else. Retailers don t have any way of tracking ownership, he says. (The lack of tracking is also why stores generally don t reimburse consumers who lose gift cards.)

Most sellers mail you the gift cards, so this strategy works best when you can think ahead. But it s possible to get instant gratification. In December, I snagged a $65 Under Armour gift card for $50 on eBay. The seller emailed me the number within minutes, enabling me to get a 23% discount on the price of a specific shirt my boyfriend requested that was, of course, not on sale. Among my other recent gift card deals: $60 in Borders (BGP) cards for 17% less than face value, and a $200 BR Guest restaurant card for 20% off.

We re featuring valuable coupons and sales each Friday to help you spend less on the items you buy. Found a deal we missed or looking for a better price on a specific item? Email me at kgrant@smartmoney.com or send me a tweet @kellibgrant.

1) Entertainment Books

Through March 31, Entertainment Books are 50% off with free shipping. We ve written about these coupon books which offer discounts for local businesses and national chains as a solution to save on expenses as varied as concerts, movie tickets and kid-friendly food. The New York book, which currently costs $17.50, has deals including 20% off (up to $25 total) at Mandee and buy-one-get-one-free breakfast sandwiches at McDonald's (MCD) .

Coupons in the 2010 editions expire Nov. 1. Keep that date in mind when gauging if you ll save enough to offset the cost of the book.

2) Marriott and Visa

Use your Visa (V) card to book a room at a Marriott (MAR) property by April 4 for a stay by April 18, and get a Visa-branded gift card worth up to $50. To get the deal, use code NAP at checkout. How much you ll earn depends on how long and where you stay. One-night stays earn $15 to $15; two nights, $30 to $50. One night at the Courtyard Dallas Market Center, for example, costs $89 per night and yields $15. You d save 17%.

3) Barnes & Noble

Barnes & Noble (BKS) is clearing its inventory of hardcover former bestsellers for children and adults, offering a selection of 200 titles (100 for adults, 100 for kids) for $3.99 apiece. Shipping is free on orders of $25 or more.

Although the site estimates saving as high as 85%, it s comparing the current price against the book s list price. Considering that many of the titles are several years old and have paperback versions, compare before you buy to make sure the additional heft of a hardcover is your best bet. At $3.99, the hardcover of James Patterson s 2007 Double Cross is 85% cheaper than its $28 list price. But you ll save 40% compared with the $10 paperback, 56% if you re a member of the store s loyalty program.

4) Dunkin Donuts

Participating locations are offering a free medium hot or iced coffee each Monday in March. (In New York, that s a savings of $1.79 or $2.79 each Monday for the next three weeks.) Don t go empty-handed you ll still pay tax. Not every Dunkin Donuts is participating, either, so call ahead and bring with you a printout of the details.

5) Expedia.com Hawaii Packages

Expedia.com (EXPE) has slashed rates at select Hawaiian hotels by up to 50%. Book a hotel and air package to save even more. For example, a trip for two from New York to Oahu in early April would cost $1,920, including airfare and six nights (already 30% off) at the three-star Waikiki Resort Hotel, as well as taxes and fees. That s $387 cheaper than booking each separately. At checkout, coupon code HVCB100 gets you an extra $100 discount (good for Hawaii packages of four nights or more when you book by March 31 and travel by April 30). You d pay $1,820 total, $910 per person, for the weeklong trip.