You can get some help from a few sites that do comparison shopping for you. Know thy merchant. If a friend had a good experience, that's probably the best recommendation you can get. There are also several business-rating sites on the Web. When something goes wrong, nothing beats talking to someone.
Most merchants list a customer-service number somewhere on their Web pages.
Know what it is before you order. In most cases, a merchant's return policy is spelled out somewhere on its website. If you can't find it or it's vague, that might be a warning flag. Most experts agree that there is little danger in using your credit card for online purchases. But your best protection is to make sure you are on a secure site - one that uses encryption technology to protect data such as your personal and credit card information.