"Nineteen-year-old Zippy can hardly believe it: she's the newest and youngest salesgirl at I. Magnin, "San Francisco's Finest Department Store." Every week, she rotates her three spruced-up Salvation Army outfits and Vaseline-shined pumps; still, she's thrilled to walk those pumps through the employee entrance five days a week as she saves to buy something new. For a girl who grew up in a one-bedroom apartment above a liquor store with her mother...