A grocer put up a sign that read "Eggplants, 25c ea. or
three for a dollar."   

All day long, customers came in exclaiming "Don't be
ridiculous! I should get four for a dollar!"   

Meekly the grocer capitulated and packaged four eggplants.
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."