If you are not using set items put them up on retainer, NPC them, or just toss them. If every person had two or three "mule" characters, that's 200-300 or 300-900 items (including all retainers!!!) not being traded on the market ward. If everyone had a surplus of items at their disposal, no one would buy anything from market ward!
There are not enough spaces and things don't sell fast enough. Honestly NOT having space is worse for the economy - especially for low and mid level gear. I would actually level weaver (which is only 11 or something now) and put low level gear on the wards if I could send items to my other characters to sell on the wards. As it is, because I care about being a culinarian more than leveling weaver, all of my space is filled with culinarian items.
It also just kills my interest in the game and stresses me out to be faced with the choice: throw this away or be able to pick up nothing more. If the markets worked better I wouldn't feel the need to hoard all my culinarian mats - but I dare you, go see what you can find for culinarian mats on the wards - they are either in small quantities, horribly overpriced or non existent.
If I could mail my culinarian ingredients to a mule I would actually be crafting more armor and weapons and taking the time to sell them. Because I have no room to sacrifice 10-20 spaces of inventory, I don't bother making those things - and there are almost never any low-level gears on the wards (and what is there is ridiculously overpriced)