> The kicker is it automatically rolls over into a paid subscription

This is how I wound up an Audible subscriber for two years without knowing. I only found out when the card I had on file with Audible (& Amazon) expired and they charged my sister's card that she had used once on my Amazon Prime account and had since been deleted as a payment method.

I happened to be in the middle of a year-long backpacking trip at the time otherwise I'm sure I would have needed to update my card info with Amazon for one reason or another and then I wonder if I ever would have noticed the Audible charges at all.