[phire]

It's not a huge amount of trust; They have your number plate on camera.

These days, most petrol stations do keep the pump disabled until a human inside presses a button. I assume the staff member is doing a quick visual check to check for anything suspicious or unsafe.

And it's not like you can't pay at the pump, most petrol stations have supported it for ages, it's just that most people in NZ would rather pay inside. I suspect the historic "fill up before paying" experience is just so streamlined that nobody bothered learning how to pay at the pump, no need to guess how much petrol you will need or risk needing a refund. And if you were going to buy anything else from the shop, it's actually faster to pay inside.