Sites that buy up or exchange unwanted gift cards have been great for consumers, says Rea. Dealing with a business, rather than an individual, gives consumers an extra bit of protection, she says. "And they're a positive thing for the gift card market."

But "there really hasn't been any accreditation or seal of approval for these exchange sites," she says. So, consumers have to take some time and do some research.

"The onus is really on the consumers to protect themselves," Rea says.

A few things you can do:

• Do an Internet search on the site name or search the name plus the word "complaints." What kind of a response does that bring? "Remember, anyone can make a mistake, Mendelsohn says."But if you see a consistency of bad reviews, then you know."
• Check BetterBusinessBureau.org for complaints, says Rea.
• Look for guarantees, says Kuadey. "If a website is guaranteeing all the transactions, whether you're buying from them or selling to them, that's a good sign."
• Don't forget to check out what's being said about the site on social networking sites such as Twitter or independent review sites, says Kuadey.

"If you don't take some responsibility to research the site, then you have to take the consequences," says Rea.