It sounds obvious: The fewer miles on the speedometer, the more the car's worth. But Allen isn't too concerned about mileage. He'll just spend way less money to purchase a higher-mileage car. "I've bought Porsches with 200,000-plus miles on them," he says. "I never worry about it. It just has to be reflected in the price. I've bought some cars that from the outside and inside you'd go, 'Oh, that car's got 40,000 miles on it.' You get in and you go, 'Oh my gosh, 200,000 miles!' But the person maintained it. They kept it up." Still, buying high-mileage cars is a bit of an advanced maneuver. You can't go wrong with a car that hasn't been driven to death. "From an investment point of view, when you're looking at what you can do to turn your money into more money, low-mileage vehicles are like a sure thing," he says. "They're only low-mileage once."