OP: +1, I don't know why it's not in there by now
I support players being able to trade whatever they have for whatever they want. I feel that if someone is forced into only trading looms for looms, much of his/her purchasing power is taken out of the equation. I sold my first LP for money because grinding looms is faster for me than grinding money (I also sold it cheaply so I could make someone happier that they were getting a deal). If the market was restricted, we wouldn't be able to use gold except for buying every single item from the shop.
I know why you'd want a 'fair' and 'even' trading system, but a free(r) trading system is what's fair. Discerning what are good trades and bad trades for you is where the work is, so make sure you pay attention and don't get screwed
Note: One thing I do not like is how you are able to list the same item in multiple trades; trading gets pretty sketchy