I've accidentally subscribed to Prime while going through the checkout a couple of times. They do make it hard not to sometimes, although I noticed a change recently, where that change and you had to opt in, not out, and the options were clearer. But my husband - who's done the same - and I have never had any trouble cancelling because you just go into your account. Although I do vaguely recall that on one occasion, we had to phone up to cancel it, which is a hassle. We've only had free trials, and they are quite nice. :)