My experience just a few moments ago.
I opted for the least expensive shipping option on an order I was placing. When I was just about to finish checking out, Amazon applied a 1-month free trial of Prime to my invoice--without my permission--and so I got free Prime shipping.
Here are the out of the ordinary aspects of my order--I don't know, of course, if one or more of them played a part in me receiving this Primal gift:
1. It was a dropship, to a friend.
2. The order started out less than $25, so I didn't qualify for free shipping.
3. I looked around for a little while, and found a filler item to bump the subtotal total over $25.
4. There was an unusually prominent banner ad, on one of more of the final pages, for a free 30-day trial. I ignored it. A little later, I copied the URL for one of the webpages with the banner ad, but I didn't see the ad on it:
https://www.amazon.com/gp/buy/spc/ha...ngJavascript=1
I consider this action by Amazon to be "over the top". I had no trouble seeing their prominent banner ad. I didn't want the free trial, _or I would have signed up for it_. Now, I suppose, _I'm_ responsible for canceling(s-p-?) my membership or I'll be billed for Prime in perpetuity?