Economist Steven D. "Freakonomics" Levitt reports:
"The fee for a trick varies with the type of sex act, and prostitutes seem to discriminate across clients in order to maximize profit. White men pay $8 to $9 more per trick than black customers, with Hispanic clients paying some amount in between. When bargaining, prostitutes will usually offer a price to a black customer but will make a white man throw out a number first. Repeat customers pay slightly less than new customers."
Too bad prostitutes can't afford to pay for Malcolm Gladwell to address them, because Malcolm would explain to them that, like car salesmen, if only the whores understood that they were unconsciously discriminating, they'd stop leaving money on the table.