Shopping for a site to sell gift cards to is just like shopping for anything else: price matters.
"Sites typically have fees," says Mendelsohn. It's "really important to read the fine print. Like anything else, it's comparison shopping."
Her advice: Pick a few reputable sites and compare what you will get back for your card. Be sure to include the transaction fee.
"That formula will give you what you're really getting back," Mendelsohn says. Do that on three or four sites -- "that's how you pick," she says.
Allow for intangibles, too. Sometimes you won't end up using the site with the best numbers because it won't have what you want, she says.