100k miles is nothing if the car was taken care of. Honestly I think that gt you posted would be a better value than the LX. Not because the insurance or appraisal companies think so, but because more people are after the gt look with the ground effects. Honestly I would run a carfax on the GT, if its clean show him 4500 cash, not a cashiers check or a money order, crisp clean 100 dollar bills. Tell him you have the money and you are ready to walk and I will promise that he bites.
