Washed plastering/rendering sand can be used internally/externally no problem. If i had to, i'd prefer sand from a builder's merchant rather than the shed,, but we're lucky enough to have a quarry near us that can supply quality plastering/rendering sand,, whether it's just the odd couple of bags, (fill your own, pay the machine operator), or get it delivered by the lorry load. I've never bought sand from any of the shed's.
I've noticed as well, that week by week, there can be a wide variation in the colour of "shed" sand too,