4. Keep your info private. Never provide personal information, including credit card numbers, on a page with an address that doesn't begin with "https" (the "s" is for "secure"). Also, make sure there's a tiny closed padlock in the address bar or on the lower right corner of the window. Type nothing personal into pop-ups. Hackers can create pop-ups that appear on legitimate shopping websites but are unrelated to them.
5. Know which emails to ignore. Never respond to emails that ask you to confirm recent transactions or try to steer you off-site (such as away from eBay after your bid does not win). Legitimate shopping sites will send an order confirmation, usually with instructions on how to track the delivery of your purchase, but they will not ask for confirmation. Messages seeking it are really after your personal info.
6. Type website addresses yourself. Don't rely on links in emails and advertisements promising to take you to a retailer's website; they could be cover to download a virus to your computer. When searching for items by keyword, carefully review the spelling and punctuation of website names listed on results pages. Scammers can easily set up a phony site that's just a letter or two different from the one you want.
7. Wait for the check to clear. When selling online with payment by check, don't ship the merchandise until your bank reports that "funds have been collected" from the buyer's check. This can take a week or longer. Although your account may show an immediate credit after you deposit the check, what's really happening is that the bank is fronting you the money pending clearance of the check. You will be liable for all money drawn from the deposit should the check prove bogus.
Sid Kirchheimer is the author of Scam-Proof Your Life, published by AARP Books/Sterling.