If you’re buying a used car in California, there’s a bigger risk than you might think. New data shows the state leads the nation in vehicles with rolled-back odometers. Carfax estimates more than 530,000 vehicles on California roads have altered mileage, accounting for nearly 22 percent of all U.S. cars with odometer fraud. Federal officials say nearly half a million vehicles are sold each year nationwide with fake mileage. On average, buyers lose about 3,300 dollars, not counting repair headaches or higher insurance costs.