I only activates prime with the 30 days trial when I bought a TV that didn't have free shipping otherwise. Canceled it the day when the TV arrived to my home.
I've done that 30 day free trial thing about three times, they caught on to me and started to make it extremely difficult to cancel. So I don't do that anymore. I just endure the long shipping times and it's no big deal. I don't need Amazon prime for anything, I don't watch movies or whatever else the heck promises they promise. I don't need it.