The point of trading is for a player to try and earn a good deal not to get a set price on something, players either want it enough to buy for more or you don't get it simply as. stupid idea.
What would change the economy would be restocking zc shop with multiple stuff some worth 20k + 10k(as last time i was on someone had 30k zc and that was while ago) + do lots worth 1k-5k melee's guns spells/powers! soon as you take most zc back out of game then the trading will become more reasonable.