Donating an old car to charity seems like a good idea: It gives you a tax deduction, helps a worthwhile case and your car can be "recycled" for a good cause. But if you ever see a nonprofit with billboard, TV or newspaper ads that make it easy for them to pick up your car and do it for you, be sure to avoid them. Those agencies are actually for-profit intermediaries that take a huge chunk of the proceeds -- up to 90 percent -- and donate the rest to the actual charity. If you want to really, truly help a nonprofit, donate directly. Or better yet, sell the car yourself and write a check to the charity of your choice.