There is a free market in the game where you can sell things.
It is located in the city of Lorencia at coordinates 134x131
Click on it and see three sections
The first section is all available items for sale and their price
Second section
Here you put the item up for sale and set the price and see all the available items that you have put up earlier
Third section
This is an exchange point for market coins (for which you buy a thing from the market or stones) and also back to W-coin, Goblin Points and also stones
Also, by clicking on one of the sections you will see the exchange price