This is just one of many tactics retailers use to manipulate consumers. Dark patterns are the often unseen web-design choices that trick users into handing over more time, money, or attention than they realize. A team of Princeton researchers is cataloging these deceptive techniques, using data pulled from 11,000 shopping sites, to identify 15 ways sites subtly game our cognition to control us.

The research builds on the work of Harry Brignull, a London-based cognitive scientist who coined the term dark pattern in 2010, and the authors Richard Thaler and Cass Sunstein, whose work on “nudges” explores how default options influence behavior. Just over one in 10 websites contain at least one type of dark pattern, the Princeton research finds. The more popular the site, the more likely it has at least one.

The most common dark pattern is scarcity bias: Put an item in your cart, and you’ll be served a message claiming “Only eight left in stock!” thereby urging you to buy immediately before the item is gone. But by analyzing webpages’ scripts and plug-ins, the researchers found that in many cases, these numbers are either generated randomly or set to decrease according to a schedule.

This theater of numbers is also key to the second most popular dark pattern: the flash sale. Major fashion retailers often tease a sudden, temporary drop in prices, crowning a page with a banner reading “Sale ends soon!” and a countdown timer. The “urgency” creates anxiety and uncertainty, pushing us to take advantage of lower prices immediately. But again, researchers found instances when the sales continued even after the timer had expired.

It’s not just the numbers that are fake—the shoppers are, too. The third most frequent pattern, “social proof,” has to do with the pop-up messages displayed on the sidebar of some sites: “90 people have viewed this item!”; “Joanne from Florida just saved on a sweater!” The tactic harnesses the power of both bandwagon thinking (This is popular, so I should get it) and scarcity (If I don’t get it, someone else will). But after analyzing the sites, researchers again found that the pop-ups come from random number generators and selections of stock messages. You don’t have to buy the sweater if you don’t want to. Joanne isn’t real; she’s just a few lines of code, and code doesn’t wear sweaters.

I’m certainly not immune to dark patterns. My personal weakness is limited to free trials—to Audible, to Starz, to Amazon Prime. I’ve been burned enough to know better, but I’m still sure every time that I will remember to delete my account before the cutoff date and avoid being charged. Essentially, I have more confidence in my future self than in my present self. That assurance that we can outwit the dark pattern is, naturally, a dark pattern of its own.

“People have excessive faith in their own memories or their own ability to come through and do something in the future,” says Don Moore, the Lorraine Tyson Mitchell Chair in Leadership and Communication at UC Berkeley’s Haas School of Business, who is not involved in the research. Moore studies how confidence influences economic behavior. “Consumers are often a little bit too reluctant to contest their own failings, limitations, or errors. And so we aren’t sufficiently anxious about the potential for manipulation. It’s common for people to say, ‘Oh, I meant to do that,’ when in fact they were manipulated.”