Well, this is very exciting news, I'm finished.
This is the main window (boring).
This is my favorite window (I can delete your items or ban you), search players advertisements (it's not case sensitive), and overall just cool (compare prices).
This is where your inventory loads in, just click the row, change the price (optional) or the Quantity (also optional) and push
Add. You can also
Remove or
Edit your current advertisement in this window.
@bloodykiller, yes you can obviously add hats, I added one to my inventory to show you.
To use the Advertisement Bulletin Board just say
/advertise.
(Contact button is the only thing it lacks).
If you think I should add or change anything speak now or forever hold your peace.