Really confused today. I placed under £3 of bits in my amazon shopping basket, trader sourced but fulfilled by amazon with free delivery if over £20 - which mine obviously wasn't.
At checkout, I was offered just one option - £0.99 for 'One day Delivery: get it by Saturday'. In my book that's five days not one, but who cares, £0.99 is reasonable and it's not urgent. Elsewhere on the checkout page I was encouraged to sign up for a one week trial of prime to get free delivery, for exactly the same sum of £0.99. I was extremely careful to not tick that link.
Anyways, I placed the order which was accepted with £0.99 for one day delivery, arriving in five days, and no Prime signup.
As an experiment and to confirm I'd not joined Prime I tried to check out the same basket of goods again, 5 mins later. Again I was offered one day delivery for £0.99, but this time they are predicting I'll get it by Monday, seven days.