Most OPS accounts are free to consumers. Given their expanding market share and the steady introduction of new ones, here are steps to ensure you get the best deal:

• If you already use an OPS, compare its terms with other OPS offerings on the market. In particular, confirm policies when merchandise isn’t delivered or arrives damaged. Also confirm refund policies.

• Check with your bank. Your Mastercard or Visa may provide a similar service that allows you to retain all of the legal protection extended to credit cards. Programs include Verified by Visa and Mastercard SecureCode.

• See where it’s accepted. Not all OPS services are offered at every retailer. Some accept only PayPal, for example. Check with your favorite sites to see what OPS service they accept before signing up.

• Verify the site’s security. Look for a black lock icon on the status bar at the bottom of the page. If the lock is closed, the page uses encryption. Double-click on the lock to show the security certificate for the site. In addition, some sites such as PayPal now offer a security key that features a constantly changing code you type in when accessing your account.

• Confirm that the OPS rocks. Before signing up, see if the OPS is offered at sites where you do most of your shopping. For example, eBay owns PalPal and currently accepts only that OPS.

• Check how cash changes hands. If you plan to send or receive cash, confirm the fees, process and timing.

• Avoid being stung. Crooks with too much time on their hands create sites that look like OPS sites. Then they e-mail unsuspecting victims telling them there’s a problem with their account and include a link. The problem is the linked site is a fake, designed to get you to divulge your user name and password. Self-defense: Never click on links in e-mails that claim to be from an OPS. Also avoid replying to the email or providing any information.