How can customers be assured the casino isn't using a magnet or some other cheating device?
With casinos it's the opposite. Their customers regularly lose their shirts. Maybe the games aren't rigged, maybe they are, as someone who regularly loses (as most gamblers do), they might as well be rigged and I would not be surprised if there was regulatory capture and the consumer would have no way to know.
And, besides, if it ever got out that a casino was doing that, it would basically fold up overnight.