How online retailers trick you into signing up for costly monthly memberships

Some online retailers (usually clothing companies. like Rihanna's Savage X Fenty) sneakily insert monthly memberships into customers' shopping carts, and if the customers don't remove the subscription from the shopping cart, they'll get stuck with a $50 monthly bill that can't be canceled unless they talk to a customer service rep on the phone whose job it is to use every persuasion tactic in the book to prevent the customer from canceling. Note that the cost of the monthly membership isn't shown in the shopping cart, so it looks like it's free.

From Nicole Dieker's Lifehacker article:

I tried shopping at Savage X Fenty, and although the website clearly stated that I did not need to become an "Xtra VIP Member" to make purchases, the site also automatically added a membership to my cart after I clicked on an item. Only after I deleted the membership from my cart was I able to begin the checkout process at the "Basic" (non-member, and twice as expensive) level-and even then, the site kept nudging me to join Xtra VIP.

As Vox notes, Savage X Fenty isn't the only retailer with these types of membership fees. Fabletics is another well-known retailer with a $49.95 VIP Membership, and although the process of making a non-member purchase is more transparent, the site still uses color and contrast to convince you to become a VIP.