There are many players in Guild Wars 2 who are currently losing gold by selling items on the trading post and they don’t even know it.
How you ask? Just by scanning the trading post you will notice that more than 80% of items listed there are sold only for 1 copper above vendor price or vendor price plus listing fee. Most players don’t know that there is an additional selling fee of 10% that is subtracted from the selling price, when the item is sold.
In this image you can see how players are clueless of how they are losing copper.
This quest item (yes you can sell quest on the TP) is listed for 1 copper with the listing fee of 1 copper, that is taken from you in advance. And if the item is sold an additional selling fee is subtracted so you actually lost money from this deal.
So the true cut that the trading post takes from you is 15% of the selling price. So if you are selling items 1 copper above vendor you are losing gold. You would be better selling the item to the vendor and getting your money right away with no additional charges.
Whenever you sell an item make sure to calculate the 15% cut the trading post subtracts from your sale. Too difficult? Guild Wars 2 Riches has posted a great calculator tool that does all the math for you and you see exactly how much you will earn. Check out the Guild Wars 2 Trading Post Calculator and see how easy it is to use.
With the current state of the game you are better off vendor selling the item or salvaging it for crafting materials. In a months time things will change and we should see the prices of goods going to a normal level.