A lot of people use the Trading Post for selling various items, but many fail to realize that this service comes with a fee. It's frequent to see crafted items / armors for only a copper above vendor value, which is lost in most cases to the listing fee.
Even worse, sometimes the listing fee is higher, now you're losing money every time you are posting something instead of just vendoring it, because of the initial 5% fee.
And when you sell your item, the Trading Post will get a 10% share of the sale,that's a 15% cut from whatever you sold, it can quickly add up...
I'm not telling you to vendor everything, but to use your brain, or at least, to use this calculator :
Stop losing money !