Concor's N gauge equipment has been pretty good, quality is ok and paint has been decent. So, if you're worried about the cars themselves and how well they will run, that is not a problem, they should be fine.
As the previous post indicates, the first question is the one that only you can answer. So, the next question is, what era are you modeling and if it's today, can you repaint the cars? If you are modeling 20 years ago, perhaps nothing needs to be done to the cars. Only you can decide that. The rest of us can only offer opinions. Good luck with whatever you decide.