Partially me, partially a previous customer
Ok, so the nearest Tesco is 24-hour, so I go there after a late shift at work, so I can sneak in goodies without the folks knowing (my mother tends to ask what I bought if she catches me).
So I come onto a self check-out just after a man in a rather smart suit, it was fairly early for me so there were a few people around, and I have trouble getting the thing working.
That's when it says 'Please take your change, notes are dispensed below the scanner.'
I look down, the previous guy left a fiver in the slot, and it wasn't budging because it was smart enough to know the fiver had been left behind.
I tell the next person what I'm doing, leave my stuff and try to catch up, but fail, as did the staff member.
The staff member said since I had been honest about it, I could keep it.