Do you get your currency back when an item is placed for sale in the trading post? Say for instance an epic “Companion” you would like to sell that would run you 12g to post for sale…if that item does NOT sell within it’s time frame…do you get that 12g back or are you screwed out of 12g 
12g to post seems kind of high or was that just an example you pulled out?
Generally the silver/copper cost to post isn’t returned if the object isn’t purchased as it was the cost for you to post it and it was. So as far as a business transaction went, they did their part.
It was 12g 50S actually to post and yes I agree that is VERY high I thought. It’s a purple item “Handmaiden of Sorrow” …yeah I think I got screwed 12g damn that’s a bummer. Thanks for the reply!
Costs are 50% of the shown vendor price. Some epic or legendary items could be sold for up to 200 g to ingame vendors and therefore cost 100g to offer at tradepost. I assume that the handmaiden has a price of 25 G shown on the item-“stats”