A better marketing approach to this would have been to silently only accept VISA and never call attention to the fact that there is an arrangement behind the scenes.
"Sir, your card is being rejected. Do you have a VISA card that I can try? It seems for the past few days, those are the only ones that seem to work for anyone around here."
This would be a bit of scumbaggery but pure marketing genius I say.
Is there any technical barrier that prevents the swiping machine from accepting another card? If so, you could literally show them that "Look, it isn't working"
This would be a bit of scumbaggery but pure marketing genius I say.