A 21-year-old college business major in New Jersey has proven a basic lesson of marketing: Sex sells. Courtney Van Dunk posted a bikini-clad picture of herself on eBay about two weeks ago, auctioning off space on her body for advertisers. The auction ended with a winning bid from a New Jersey wine retailer, who offered more than eleven-thousand dollars for a month's worth of advertising. But even though that offer has been retracted, Van Dunk remains confident that she has made contacts with enough companies to still earn some cash. She got the idea from a marketing class she took. When Van Dunk finds a buyer, she'll put temporary tattoos on her abdomen while she's at the beach. They also may go on other body parts when she's at the mall and other public places. But her butt and chest are off limits.