a missfire will not sound smooth on idle or under power. basically one of the cylinders won't be firing properly. depends on how bad it is. slight might be seen as an overly vibrating engine. bad and there will be smoke no power etc.
If you want to test drive a car i would suggest going to a main dealer. Find one locally with a 320, this will be a far better reference. CarGiant is not picky about the cars they buy. You've seen the adverts we buy any car. This is where they go among others. A friend of mine bought a golf from them. It was very dirty and poorly prepared and when i checked it over it had not been serviced for 30k. Needless to say it was not the most reliable thing.
E90 330i SE Auto Graphite Grey Metalic