The 14 3/4" flat car is a scale flat car that is most likely selling alright. The closest scale flat cars are PS-4 flat cars produced by Lionel or the O scale flat cars produced by MTH.
These Pullman-Standard 50' box cars have already been out on the rails for 30 to 40 years. They would be producing a model of a still active type of box car. The real ones will only be around 10 to 20 years before being replaced by another type of car.
Anderew