Dark patterns are tricks used in websites that make the user do things that he or she didn't mean to, like subscribing to a newsletter or buying something.
A common dark pattern when registering with a service is a series of checkboxes with alternated meaning. For instance, ticking the first one means "opt-out," and the second means "opt-in".
It's called a roach motel when it's easy to get into a particular situation, but then makes it hard to get out of it (e.g., a subscription).
When the website asks for your email or social media permissions pretending it's going to use it for finding your friends. Eventually spamming all of your contacts and acting to be you.
Bait and switch
There is a sign of bait and switch when the user sets out to do one thing, but a different, unwanted action happens instead.
Disguised ads are adverts blended into the page in such a way that it looks like it's part of the content or navigation. With the sole purpose of tricking you into clicking on them.
Sneak into basket
This dark pattern occurs when you want to buy something, and the site sneaks an additional item into your basket.
Misdirection is the act of purposefully focusing the user's attention on one thing to distract their attention from another.
There is a sign of FOMO (Fear of Missing Out) when users are tricked into thinking an item is in high demand. This puts them under pressure to make a quick buying decision.
Confirmshaming is when you make a user feel bad about opting into something. The option to decline is designed in such a way that the user shames into compliance.