You can use the @market command to create a clone of your character that will display a market title and a market message. When players double-click on a market title, the market's message will be shown in the chat channel in the font color chosen by the player.
Format: @market "Brief Market Title" "Market message can be longer and more detailed." colornumberhere
Usage: @market "S>Bloody Branches" "1k BB for 400 plats" 14
Q) How do I close the market?
Q) Can I go @afk after I @market?
Yes, you can. Just make sure to @afk in the AFK section that's in the upper-right area of Moonhaven.