After a Forbes contributor spent $500 on a secondhand Louis Vuitton bag but couldn't tell if it was real, Forbes' personal finance writer Deborah L. Jacobs waded into the murky world of counterfeit designer bags to find out how to spot a fake. She spoke with Susan Scafidi, who heads the Fashion Law Institute at Fordham Law School, and picked up some valuable tips for anyone looking for a designer label at a bargain price.