Self-paid machine

I went to NTUC with my auntie today, and I saw a self-paid machine. it's a little bit strange to me because there's no such thing in my country. So, I tried to use it.

I think the made this machine to avoid long queue, because there are so many people who go to NTUC and buy something. And also because they do not have enough quantities of counter.

I wonder how they trust someone so easily. What if there's someone who intentionally try to cheat with the payment.