Merchants are special characters. You can order items from the Blacksmith, Fortune Teller, and Inventor.
For a fee, they will craft talismans and items that you will need for trading with residents and completing quests. The fees for crafting items are paid in coins and reagents (Runes, Flasks, Flowers, etc.).
In the "Exchange and Reagents" section of your inventory you can only see the number of items you have. Go on the map to the Blacksmith, Fortune Teller, or Inventor to craft various items using reagents.