I would agree with most of what you said Mercman, but I don't think crayon mark are "fair wear and tear" and whether I would charge someone for this would probably depend on how long they were there. I had a great tenant who moved after 3 years and about 2 months before she moved her daughter used the wall to express her artistic streak!! I didn't charge for this as I needed to repaint the walls anyway....however, if a tenant was only there for 6-12 months after it being freshly painted, I probably would charge.
However, as the property has been sold as is (I doubt he is going to actually repaint before handing over the keys), it probably is unfair to charge.