When I was 12, I was playing a game, and an 8-year-old came and put his quarter on the bezel above the control panel.
"Sweet - thanks!" I pocketed it.
He ran off, yelling "mom!", almost crying. He came back with mom, who asked if I took his quarter.
"Oh, that was his quarter? I'm sorry, my mistake." Mom gave him another quarter, and left.
He put his new quarter on the bezel above the control panel.
"Sweet - thanks!" I pocketed it.
He yelled at me this time. I replied, "Look - it costs 50 cents to play this game, yes?"
He hesitated, then answered: "Yes."
"Right", I said. "So, thanks for playing."