Look at the windows and check that they are all the original, of one make eg Pilkington, Sekurit etc ,
If it has been in a bad smash and then repaired Cat 2 writeoff then it may have odd windows.
Check the number plates. If they have the name of the original garage that sold it new, that can be a good sign. If the front is new then maybe the car has been in a front end smash (maybe not , could be just a new plate).
There are plenty of things to look at before getting in the car or even starting the engine.
If it is raining and the car is wet then come back another day in the dry and look at the paint, do all the panels colour match if not walk away or run away if you prefer.