it can be adjusted. if TNB meter can be tampered, why is the mileage meter unable? just rely on the mileage is foolish.
get a good mekanik and together evaluate the car.
inspect the rubbers, under the mat, boot area, and under carriage.

as for the engine, only a test drive can evaluate.

even so, buying a used car is always higher risk. but u pay much less.
so GOOD LUCK