[Milly]

If you try to put a card on a vendor (in a building, haven't tested with outside vendors), it takes an inventory slot from you first.
It says this:
You have placed Tailor - 1 / 1 * for sale at Alfredo.

You have set the price of Tailor - 1 / 1 * to 100c.

You pick up Tailor - 1 / 1 *.

If you close out the vendor and reopen it, the card is there!
If you close out and reopen your inventory, the card is there and is now missing from the vendor (as well as the appropriate slot in the shop)