Price Discrimination for Eyeglasses
A firm engaged in price discrimination faces two practical problems. The first is the problem of distinguishing customers who will buy the good at a high price from those who will not. One solution is said to be used by optometrists. When the customer asks how much a new pair of glasses will cost, the optometrist replies, "Forty dollars." If the customer does not flinch, the doctor adds "for the lenses." If the customer still does not flinch, he adds, "each."
~David Friedman's Price Theory textbook (copyright 1990)