So I did the free trial of amazon prime in december and only ordered a couple of items, which arrived to my house within the next couple of days. I have two friends who asked to use my account for the free shipping, so I let them because why not? The first ordered a couple of items with an Amazon gift card. The second friend ordered a couple of things with her debit card. I'll mention that all of these items weren't expensive at all, and I received a series of emails each time something was ordered from my account.
So a month went by and I was never sent any emails or notifications of any kind that my free trial was about to expire/expired. One day, a third friend asked if I still had prime but I was unsure. Whenever I was on amazon on my laptop or my phone I never received warnings of any kind. Just to be safe, one day in January I logged onto my amazon account on my phone and cancelled my prime membership. After the page said it was cancelled, the website refreshed to the home page. Again, I was never sent an email or notification, or anything, so I just assumed it got cancelled and kinda forgot about it.
A few weeks later, in February, my second friend, the last person to use my account with her debit card, got freaked out because her card, that had less that $10 on it, was charged with $116 from amazon.com, plus overdraft fees from her bank.
I was never informed that my free trial was over and that one of the cards on my account was being automatically charged over $100.
The card that was charged was my friend's, it was under a different name, and it was not the main card that was connected to my account.
I logged onto my account on my laptop to see that her card was charged in January yet she didn't receive a bill until almost 3 weeks later.
I cancelled the membership on my phone, yet it apparently didn't go through properly. And I was, conveniently, not notified about anything.
I cancelled my membership, successfully this time, on my laptop and am in the process of getting a refund to my friend's card.
I am still very angry that I was never informed about my prime membership becoming official and charging me $100, yet they can inform me about "This week's deals!" so easily... hmm... okay.

I have actually come across multiple people who have had the same situation happen to them.