How do I take a listing down?

Changed your mind, or it sold elsewhere? Just change the piece's status away from For sale / For trade — set it back to Delivered (or whatever fits). That removes it from the marketplace immediately.

You don't have to mark it Sold to delist it; Sold is only for items that actually sold and that you want a record of. See How do I mark something as sold?

If it was part of a set you listed, adjusting the set's status will bring its members back in line too — see How do I sell a whole set?