actually you know some of the free stuff that you get from games/daily chance/quests sell well also. always check the price on the marketplace first (but what the people are selling it for, not the average sell price), then the price that you get from selling the item in the store (if it can be sold there) and then sell the item for the higher price of the 2.
if you have to sell it on the marketplace then sell it for at least 10gg under the lowest buy only price.