This artwork is discounted because of a red signature ghost and a tiny fiber (maybe a brush hair) inside the paper. You can see the red ghost to the right of the actual red stamp in the image above. The fiber hides well.

If you are wondering, red ghost refers to a red shadow of the artist's red signature stamp. This is sometimes transferred from a previous painting which happens when the artist signs all of his work at the same time and piles up the paintings before the red ink is dry. It's more common than I would like, and it costs me a lot of money - but I am picky about quality, so my loss is your gain.