I see trading here as a 'bartering' economy, rather than a 'currency' economy.
Bartering by nature is subjective in its allocation of value: what is valuable to one may not be valuable to another, yet both items have some level of value in the system. That value changes, however, with nearly every transaction. Say I make a lot of wooden widgets, and I offer 1000 widgets on the open market with the stipulation that I want 1000 steel sprockets in return; my neighbor makes sprockets, but he also has a cousin who lets him have wooden widgets at wholesale. So my widgets aren't as valuable to him, and he may decide to pass on the offer, saving his sprockets for something that he really needs. I might be able to get him to trade, but only if I increase my offering amount, say to 1500. Now he might take them, as they are about equal in value to the wholesale ones his cousin Shecky gives him.
Meanwhile, another neighbor crafts marble doohickies which, truth be told, are in short supply in my house. She is offering 1000 of them for 1250 widgets (I see she also has a listing for the same 1000 marble doohickies for 1250 sprockets). At first glance, this doesn't seem to be a "fair trade" within the bounds of the "Barterer's Code", since she wants more (value) than what she is offering. However, I really need those doohickies (they have higher value to me) and I swap my widgets for her doohickies. My neighbor, though, has another cousin who gets him marble doohickies at a song, and he thinks she is over-valuing her doohickies, so he doesn't trade his sprockets to her either.
As you can see, all 3 items (widgets, sprockets and doohickies) have the same intrinsic value within the Barterer's Code"; yet they can be traded at differing artificial values depending on what each trader considers them to be worth.
OTOH, in a 'currency' economy, the widgets, sprockets, or doohickies would have a universally accepted value, equal to a set amount of currency (coins, supplies or self-produced goods). In the above example, I wouldn't be making an offer of my own produced goods, I would look to the "Buyer's Price Index" to see how many of the 2 items I cannot make could I buy for what amount of my own widgets. The Index tells me for 18,000 widgets, I can buy 5,000 sprockets or doohickies. No more, no less. There is no negotiating with the Index. It also tells me that, for 400,000 coins, or 125,000 supplies, I can get the same number of sprockets or doohickies. But the Index has no price for widgets, because I am cannot buy what I already make.
Here, all 3 items (widgets, sprockets and doohickies) have the same intrinsic and artificial value, and neither value can be altered during the trade. This is the function of the Wholesaler booth in the Trader.
To sum it up, Trading through the Trader is, for all intents and purposes, bartering. Each barterer decides for themselves what the value of the goods are, both theirs and those of the other barterer. As there is no set value for the items, trades can be as equal or as lopsided as the 2 participants are willing to allow. If each is satisfied with the end result, who are we to tell them that they committed an infraction?