i beleave there 2 be no such thing as "pristine" anymore but on the other side of that, you can introduce parasite, virus, or some other bad thing....
exsample, about 5 months ago i get some sand from FL beach, thought just drying it out and cleaning it well would be good enough.
turns out in introduced Pyamid snails parasite, wasnt hard to deal with, really (due to the size of my tank) but i could imagein that something else could really sux, in a larger tank where you couldnt get to all the snails to clean.
its a toss up, your safer just buyin it new