Also you can calculate the mileage by asking few question without letting owner know about it for .e.g. in your case it is 89000 kms for 2009 car, which means 6.5-7 years old car, around 12.5-13k kilometers in an year, this mean around 35 kilometer daily. you can ask the owner about his daily travel, highway travel extra and calculates if his answers are matching to the overall mileage.