Harry Brignull has spent some time collecting and contemplating "Dark Patterns" in online commerce, the unethical, manipulative, and sometimes outright deceptive things companies do to try to manipulate customers into things they probably didn't want to do.
For example: the form that has a "sign me up for email marketing" checkbox in tiny type at the bottom you need to find and uncheck if you don't actually want to sign up for spam. Brignull has examples that take this to an appalling (and hilarious) extreme.
The full 30-minute video shows the evolution of Dark Patterns and offers some insights into why companies persist in these customer-unfriendly (and sometimes illegal) tactics. Brignull maintains a website with a catalog of Dark Patterns he's collected over the years, and it's well worth browsing.
Coming from a Customer Experience perspective, I think it's especially useful to think about how Dark Patterns come to be, and how they illustrate some of the challenges in trying to design and implement outstanding CX. Dark Patterns almost always involve either misleading the customer or making it hard for the customer to do something (like cancel a subscription). The end result is likely to be an upset customer (or former customer) and very poor CX.
By the time the customer gets upset--when she discovers she's been fooled or trapped--the company already has what it wants. It's too easy for the company to think that CX doesn't matter, because the short-term metrics (sales, newsletter subscriptions, etc.) don't adequately capture the damage that's being done to the customer relationship.
So while you may be able to boost the percentage of customers who buy travel insurance over the short term, those customers aren't going to be happy when they discover the extra charge. They probably won't be fooled a second time, and may take their business elsewhere or warn their friends. Some may call and demand refunds.
In extreme cases, government regulators may get involved.
In most cases, CX professionals who are doing their jobs properly will be working against Dark Patterns. The challenge, as it so often is in the Customer Experience world, is to help the rest of the organization understand that while manipulation, deception, and intentional barriers may sometimes improve short-term metrics, they rarely pay off in the long run.