How do I cancel or lower the price of a listing?

Lower the price: open the listing and choose Edit price. The new listing is a fresh signature and costs no gas. The old, higher listing is superseded on Unvault.

Cancel: choose Delist on a fixed-price listing, or Cancel auction on an auction you created that has not settled. Cancellation is an on-chain transaction that costs gas.

Why on-chain? A fixed-price listing is a signed message. Hiding it on the site does not destroy the signature; only an on-chain cancel (or the expiry) makes it unfillable everywhere. If you want certainty that an old listing cannot be filled, cancel it on-chain — or transfer the item to another wallet, which also invalidates listings for it.