Positive feedback; On eBay, where buyers are quickly becoming sellers and sellers are turning into online boutique owners, fashion follows its own rules.

Byline: Irini Arakas

Carolina Herrera, Jr.'s, first time was in South America. "I was on winter holiday," she recalls, "and very bored. I logged on to eBay and discovered the most exquisite nineteenth-century settee." It now lives in her Madrid apartment. Katy Rodriguez, of Resurrection, searches for Versace Home (especially the opalescent Medusa wine stoppers) and quirkier home-inspired items: "My holy grail was a sixties Campbell's Soup dress with the original hanger." Claire Stansfield, co-owner of Rellik in London, searches for Ossie Clark and Biba. And social doyenne Vanessa Getty recently purchased a late-70s Yves Saint Laurent crystal "nugget" belt for $800. Everyone has an eBay story: her preferred searches, her auction-grabbing techniques, the sandals she won, the frock that got away. But recently, the narratives have been shifting. Buyers are becoming sellers; sellers are becoming boutique stars: and just what is being bid upon online may also be redefining what sells at brick-and-mortar stores across the globe. eBay sets and follows its own fashion logic: That hot motorcycle bag you bought from Balenciaga in turquoise will fetch low figures come bid time; in shell-pink, however, it could earn your money back and more.

"We are always looking to 'grow the business,' " says Tia Miller, vice president of lifestyle for a company that has taken in more than $3.1 billion worldwide in clothes and accessories this year. "We think about conversion rates, percentage of listings that are actually sold; we track denim lines; right now, Habitual, Citizens of Humanity, and True Religion are in high demand. We think about the next UGG craze." Mercifully, there isn't one.

But what items have lasting value and resale potential? On eBay, the answers don't always come from the more obvious fashion sources. Style director Constance White explains, "eBay is almost impervious to outside commercial forces; it has its own fashion barometer." Yes, as in the rest of the style-conscious cosmos, the Fendi Spy bag is a most-wanted; log on and you will find more than 60 selling for upwards of a grand. But you will also find Luella Bartley's Gisele bags from last spring in heavy bidding wars. The Luella bag is what Lisa Jacobs, fashion director of Portero (a new online company that resells luxury goods through eBay), deems one of "the new classics." (Portero, in the limited language of fancy consumerism, is ...