OK here is how it happens. When you put stuff in your basket there are two prices, some items are exclusive to prime members and they only have the one, prime price. Thus add these to your basket and you are signing up for prime if you do not opt out. Often if you do opt out some items will be flagged as no stock or prime only. They hope I imagine that in order to get the items, you will take up their offer then forget to cancel the free offer in time. its called Marketing. Its the old carrot and stick again.
At least its up front. I can remember the day when certain companies who exhibited at |hi If shows engaged scantily clad ladies to actually get you in and sign up for their new products.
I don't think Amazon have quite gone this far though I do wonder what the world would make of some more, erm, dodgy fringe benefits to Prime might be! They also want me to sing up to a free three months of Music, but I see its price is double what I refused to sign up to at the start of Alexa. Also a number of skills that we had for free, one which says it can listen to your house for burglars using AI, has now become subscription only. Well never mind I did not really want them to listen to me anyhow.
No they are all the same. Apple Music actually looks a better deal via the I phone as there is more of it. I'm not bothering though, as I want control of my expenditure and am not going to pay a monthly fee for something I may not use for some weeks as I am in a quiet mood. I prefer in this kind of thing to buy physical media, or a download outright to keep and do as I wish with, not rent a service no mater if I use it or not. Its bad enough when you sign up for a sim card for a phone you get little data, but when you have been with them for a year they fall over themselves to offer benefits. Indeed in this they are the opposite of ISPs who treat their customers as cash cows. Brian