1. Make sure that you're entering your payment details on a good site. Try to find "https://" inside the URL of the site that you're trying to buy something from. If you don't see that or no indication of any website security, then it's probably a great idea not to trust those people along with your account information.
2. If you find a fantastic product on your favorite site, search for it in the search engines before you buy it. Make note of the model number or brand, and do a quick search to make sure you can't get it cheaper from somewhere else. You might be able to save a few dollars like that.
3. When you are searching for a place to buy a product and none of the results seem to be from familiar retailers, you should be hesitant about entering your data. Look for security signs from Verisign or Cybertrust, which means you know the retailer is not out to take your money.
4. Call the web company before making a purchase. In case you have some kind of problem with your purchase, you want in order to know that you could reach customer support easily. That's why it's a good idea to call before you give them your credit card information. In the event you can't get anyone on the telephone, steer clear.