There are things you shouldn't buy online, and there are also shady-looking sites you shouldn't buy from. You probably have dozens of reputable sites in your mental online shopping database, but every so often you'll come across an unbelievable deal on a site you've never heard of. Maybe the site will seem legit, but often it won't. Most of us have good enough radar that we immediately know a bad place when we see one. Outdated site design with an overwhelming variety of fonts, item descriptions in broken English, no contact information — these are the signs. No matter how good the deal is, just steer clear.
Another red flag is a lack of security. If you reach a page on which you need to enter payment or other sensitive information, always check if the URL begins with "https" instead of "http." No "s" means the site hasn't been secured and your information could be at risk of being stolen. Get out of there quick and don't look back.