If they are a demo ski can you not try them out to make sure the size is what you want? Tey should be good but always try if you can.
It also depends where they were used Nd how much. If they were looked after and maintained then buying a demo ski makes sense. It's the same ski a you would buy. The bindings will also be the same as production models just with adjustable plates but you can often convert them to regular mounted bindings if you wanted.