The best interaction I had with one of these machines went like this. It said 'Press button to start'. I did. It stated 'now giving back change' and proceeded

The best interaction I had with one of these machines went like this. It said 'Press button to start'. I did. It stated 'now giving back change' and proceeded to dispense 17,xx€. I was then able to scan my items (2 jars of jam) and pay for them (~4€) (and got my change back too). Fantastic interaction, really. I gave the wrong change back to the cashier in the other lane though. I'm not sure how often that happens, I could have taken the money and just left, easy.