As Super Dave suspected this is digital art. The "Find Edges" filter is a standard feature of Photoshop. There's nothing wrong with creating art this way, in fact the Find Edges can produce some amazing images. But absolutely the artist should be straight about their process. Even if a printout was worked on by the artist with pencil and/or charcoal.

Or is this actually photoshop filters of the same type? Just curious, because in looking at your "artwork" it looks a bit digital to me, and not with an actual pencil and charcoal. If these are digital images, you should really say that in your description because it is very misleading to the buyer.

"Super" Dave