Half of the benefit of shopping online is the ability to easily compare prices across various sites in order to get the best deal possible. But, unsurprisingly, there’s a good chance that even after all that hunting you did to find the cheapest DVD boxset was for not. Why? Because of a particularly unscrupulous practice called “dynamic pricing,” in which online retailers will change prices for various items depending on a customer’s personal information, such as location, known spending habits, and even visiting price comparison sites.

Despite sporadic coverage of this phenomenon over the last decade, its a practice that remains fairly widespread. Since most people don’t even realize that this is possible, its also extremely unlikely that it will stop anytime soon. Luckily, a few simple measures can help guarantee that the price you get is the price you want.

Browse Privately/Incognito

One of the preferred ways of learning about a user’s income level and purchasing history is through the use of cookies. These pieces of data are what websites use to garner information about your browsing history in order to remember a user’s previous activity on the site. Third-party cookies, however, are almost never your friend. Websites can use these to view your spending habits from other websites and then adjust their own prices to get the most money out of you possible. To prevent this, simply try browsing in incognito/private mode on your browser, or block all third-party cookies in your normal browser settings.

Change Your Zip Code/IP Address

Ever wonder why online stores ask for your zip code? As it turns out, its in order to gauge your likely income level in comparison to the average level of affluence in your area, which is bad news if you happen to be a student at NYU. So if you live in a particularly well-off neighborhood, try entering in zip codes for other, less opulent areas and see what you get.

Zip codes are only half the battle, however. The second way that websites learn about where you are is your IP address, which is, unfortunately, slightly less easy to change. Certain browser extensions will assign you a new, random IP address, but the most reliable method is through use of a virtual private network (VPN), or setting up a proxy server. Either way, changing your IP address will not necessarily be an assurance of getting the best deal possible, but it will at least indicate whether or not a site is changing prices on you.

Check on a Mobile Device

As more people are now logging onto the interwebs with mobile devices than they are with laptop or desktop computers, it was only a matter of time before certain sites would take advantage of knowing whether you’re on the go rather than sitting at your desk and charge you more accordingly, or vice versa. Not only that, but certain sites will also charge you more depending on whether you’re using Windows or a Mac.

The easiest way to check how your price may differ from device to device is simply through checking on both a desktop and your smartphone/tablet. But if you don’t have a mobile device, the only way to see what is offered for mobile is by changing your user agent. This little trick allows you to fool websites into thinking you’re using a different operating system than you actually are, and can be done on any browser. For an indepth guide on how, check out the guide assembled by the folks over at Lifehacker.