Ideally do not make this deal. In case you must for some reason, take a trusted mechanic with you. Start the car without pressing gas pedal, if it starts, engine is (more or less) in good shape. Look at exhaust pipe, no smoke should be coming out. DO NOT waste time knocking on the car here and there to guess whether the paint is original or not, etc.
Drive if possible. Take left and right turns. Drive slow and fast. While driving concentrate on sound and feel, rather than anything else.
Ideally check it during the day, in moderate sunlight.
Those are my two bits.