If you and your friends shop online, you may not be paying the same prices for the same items, even if you shop at the same online stores.

That’s because online sellers can target prices to individual customers as easily as they target ads. It’s called personalized or sequential pricing. Here’s how it works: Economist Cary Deck says that online shopping leaves a data trail that companies use to predict which items you want to buy the most. Their best source of information is what you’ve put in various online shopping carts – especially the ones you fill, and never purchase. And when items appear multiple times in your carts, retailers get clued in to your tastes and interests. Which means, the drill you examined a dozen times might cost you a hundred dollars, while your impulse-buying friend got the identical drill for $10 less. But get this: You’ll BOTH pay more for related items, like drill bits. That’s because a lot of companies automatically raise the prices on accessory items once you make your first “shopping cart” selection.

And consumer law experts say the practice is legal.

After all, it’s no different than airlines and car dealers getting different amounts for identical plane tickets and automobiles.

But there are ways to protect yourself from sequential pricing:

  • First: Clear your computer cookies before you go shopping. That way, the sites you visit can’t see the items you’ve previously looked at.

  • Also: If you visit coupon sites, use the “private browsing” option on your computer. That’s because a lot of sites lower the discounted amount for veteran couponers, and offer a higher percentage off to newbies.

  • Finally, know this: Difficult customers are often targeted for premium pricing. So, limit returns, and don’t complain unless there’s a real problem.