http://www.havenandhearth.com/forum/viewtopic.php?f=35&t=31356
Check link under point 3. To shorten it up, everyone uses value for certain goods, so it easier to value up any trades that ocur. That is why most traders have similar point value of forgables, pearls, etc + have put their own value on their goods for how much they are selling it.
Hope it helps.
. Note that this is my crafter. Don't post your answers here, instead after trade with me you will have the chance to answer the question and in case of correct answer i return half of your payment (50%). Good luck