Well, the transmissions tend to last 150,000-200,000 miles(the first transmission on my car was replaced at about 125,000 miles). Interior is a big indcator, except if the car has been outside in a hot and sunny environment. The suspension components are also a good indicator of Mileage. Engine wear and related components can be another indicator of actual mileage...The best indicators for Mileage would be detailed records with every single oil change and every nut and bolt losened and tightened on the car...