For the most part I have found trading to be pretty simple and easy on the forum. I have noticed a group who will ask for more than what I think is the correct price for an item... or maybe they just 'value' the item more than I do. I'm a collector of things... not a trader per se. I enjoy having at least one of every item in the game. Because of this, I can be patient to acquire those items.
What I love are unrequested advice notes in your direct message box about how you are low balling or high balling an item. I figure if I offer something and the person accepts or says 'nah', then who cares. The transation is between me and the other person. There will always be someone, at some time, who is willing to give up xxxx for yyyy if paid zzzz. Just like the group above asks more for the items they are offering, sometimes I value that item less or more depending on my personal taste. I do not need help trading... and especially unrequested advice.
Only thing that really does make me mad is when someone offers for something you have, promises to trade on xx day, then fails to actually go through with the trade. I do not see any means of getting this corrected, even though the person has also promised and fallen through with another trade as well. I wish there was a means of reporting xxx person for promising (and promising and promising and promising x7 days) yet not delivering. (off topic sorry)