Gas station slot machines

I've been here a long time but I don't know what is up with the slot machines at gas stations? At my nearby little no-name convienience store they have a set of machine in the front and also a section in the back. The signs say "absolutely no cash payouts" but I see the same people in there in the am and the pm. I also saw a guy pull out 500.00 to play. So what is it? How does it work?

What's the protocol to start playing? I don't have any interest in it but to me its like the nude modeling studios – I know they're doing more than just looking and I know they're not playing for stuffed animals.

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