A grocer put up a sign that read “Eggplants, 25¢ each — three for a dollar.”
Meekly the grocer capitulated and packaged four eggplants. All day long.
The tailor next door had been watching these antics and finally asked the grocer, “Aren’t you going to fix the mistake on your sign?”
“What mistake?” the grocer asked. “Before I put up that sign no one ever bought more than one eggplant.”
With a hat tip to Rick Segel, I believe.