6. The deal's not done until you drive off in your new car.

You don't have to be a jerk about it, but you should be on guard throughout the entire car buying process. The biggest place that people err is when they have struck a deal with the salesperson. They breathe a sigh of relief and think the dealing is done. But the buyer needs to stay alert for the F&I process. Extra charges can appear in the contract. There may be a problem with the condition of the car. All these things can be addressed if you have the right attitude. If anything crops up during the F&I process that doesn't jibe with your numbers you can still walk away from the deal.