1. Read customer testimonials before you buy anything. People are more than happy to complain about bad service online, so look for sites and testimonials which are terrible so you are aware what you're getting into. You ought to take bad reviews having a grain of salt, but if you see many, you know there exists a problem.
2. When you are shopping on the web, you should only shop at reputable stores. If the store does not have a good reputation, you may be requesting trouble. Some people have had their credit card and personal information stolen from shopping on lower than reputable websites. Be careful and protect your private information.
3. Make it a habit to register for price alerts. It goes even for purchases that you've recently made. Price alerts will let you know when a product has dropped to some price you prefer. And if you've recently purchased at full price, you can ask for a price adjustment to meet the new deal.
4. Ensure that you're entering your payment details on a good site. Search for "https://" within the URL in the site that you're attempting to buy something from. If you don't see that or no indication of any website security, then it's probably a wise idea not to trust those people with your account information.
5. Pay close attention for potential sales online starting as soon as Wednesday. Many brick and mortar stores do sales on the weekends, and to compete, many internet retailers have moved their sales days up by a few days. You can often find exceptional mid-week bargains with just a little online research.