Each individual artist has his or her own policy as far as Terms of Use on free printables. As an artist myself I will do my best to respect the integrity of fellow artist's work.
Here is my own policy for each printable on my site:
All files and printed materials may be used for personal use only. None of the materials may be redistributed without the original artist's permission. This includes, but is not limited to sharing, selling, reselling and altering.