Sure, it sounds basic. But it pays to double-check those URLs. Otherwise, you risk landing on a look-alike site that could be anything but what you need, says Karen Barney, program director at the Identity Theft Resource Center.

Before you start shopping, check out the site's privacy and security policies, too, she says. Do they make it easy to view, or do you have to really search for it?

Pay particular attention to seller protections regarding your payment, Barney says. If you don't receive your money, do you deal with the site? Or does it pass responsibility off to a third party such as a money-transfer company?

Also, make sure you have "a good understanding" of how the site works, says John Breyault, director of the National Consumers League's Fraud Center.

That includes what happens when things don't go as planned, he says. "What's the dispute resolution process if something happens?"