You’ve installed that handy little toolbar that promises to scan every checkout page and magically drop in the best promo code. It feels like having a clever friend who never forgets a coupon. But before you let it run wild on every site you visit, there’s something you need to understand about how these extensions actually work. They are not neutral helpers. They are businesses, and like every business, they have bills to pay. When the service is free, you aren’t the customer. You’re the inventory.

The most obvious hidden cost is data collection. Every extension that auto-applies codes needs to see the pages you are visiting in order to do its job. That means it knows what you’re browsing, what you put in your cart, how much you spend, and which retailers you trust. Some extensions share this data with analytics firms and marketing partners so they can build a profile of your shopping habits. That profile gets sold to companies who use it to target you with ads or even to adjust prices based on your perceived willingness to pay. The convenience of saving twelve dollars on a toaster might end up costing you hundreds later when you are shown higher prices for products you were likely to buy anyway. Sure, most reputable extensions have privacy policies, but those policies are long, boring, and rarely in your favor. You need to ask yourself if the five dollars you save on a pair of sneakers is worth letting a third party track your every online move.

Then there is the issue of which coupon actually gets applied. These extensions often operate through affiliate partnerships. When you make a purchase after clicking through an extension, the extension’s owner receives a commission from the retailer. That commission can vary by code and by store. Some codes are tracked to the extension itself, while other codes belong to different affiliate networks. Your extension typically won’t show you every available code. Instead, it will apply the one that generates the highest payout for its parent company. In many cases, that payout code is exactly the code with the deepest discount too, but not always. A retailer might have a ten percent off code that is exclusive to a competing coupon site. Your extension could easily miss it because it has no financial incentive to look there. The result is that you think you are getting the best deal, but you are only getting the best deal the extension can monetize. You are one algorithm’s version of a bargain hunter, and that algorithm is secretly working for someone else.

Even worse, auto-apply extensions have a nasty habit of overruling your better judgment. Say you have a legitimate code that you got from the retailer’s own email list, one that gives you free shipping and a twenty percent discount. You install an extension, and the moment you reach checkout, it fires off a different code that appears to work. You assume the extension has done the math, so you click confirm. But that code might only give you fifteen percent, or it might remove your free shipping because it cleverly changes the order terms. The extension doesn’t care about free shipping. It cares about getting its referral credit. You end up paying more than you would have if you had simply typed in the email code you had sitting in front of you. This is the quiet danger of automation: you stop thinking for yourself. You trust the robot, and the robot trusts its bottom line.

What can you do without abandoning these tools altogether? First, treat every auto-applied code as a suggestion, not a verdict. Before you hit purchase, take a quick look at the discount shown. If it feels lower than you expected, delete it and manually try the code you brought along. Second, do a five second search for that retailer’s name plus “coupon” on your own, then compare. That takes less time than you spent reading this paragraph. Third, disable the extension on any site that is not a store. There is no reason for it to be active on your news feed, your bank account, or your social media. You lose a little convenience, but you gain a lot of privacy. Finally, periodically review what data the extension has collected. Many browsers let you see what each extension is able to access. If something looks invasive, uninstall it. There are dozens of these tools, and you can switch to a less nosy one in a minute.

The bottom line is that auto-apply extensions are not evil, but they are also not your friends. They are middlemen who profit from your purchases while wearing a cape of convenience. That doesn’t mean you have to throw them out. It means you have to keep your eyes open. Use them for what they are good at: catching the codes you would never find on your own. Just don’t let them be the final word. Every once in a while, the old-fashioned method of searching for a code yourself and typing it in wins. And when it does, you’ll be glad you trusted your own instincts instead of handing over the wheel to a piece of software with a hidden motivation. Save your money, but don’t lose your judgment in the process.