It's one thing to swap gift cards at the office with someone you know and see every day. It's another to go online and trade or sell gift cards to an individual you've never met or put their check into your bank account.

"There's a lot of fraud involved in that," says Kwame Kuadey, CEO and founder of GiftCardRescue.com, a site where consumers can buy or sell gift cards. "You're going to mail your $100 card to someone, hoping they'll mail a $100 card back."

Instead, he says, stick with business-to-consumer sites where you can thoroughly vet the site, its policies and its customer service record before you send off your cards.

For gift cards, "my advice is to steer clear of" the consumer-to-consumer auction sites, Rea says. And do your homework, she says. Consumers "need to do their due diligence."

Business-to-consumer exchange sites are a great resource, and dealing with a business rather than an individual provides "an added layer of protection for consumers," Rea says.

Two smart moves: Deal with well-vetted, respected sites and research before you sell.

Look for sites that offer a phone number to call if you have problems, says Mendelsohn.