On dragon chat this morning on Chaos, we batted around an idea and came up with two possible permutations:
a) order consigner - a player places an order at a central area (bulletin board, person, orb, whatever) for a specific item, how many they want, fee for service taken out at the time as well as the payment that will be given to the player(s) who fill the order. Anyone may fill that order or partial order and receive payment as set aside by the player for what they've done. Item appears in the player's vault to prevent using this for extra storage. (Note that this might overstuff a vault similar to what currently happens with items that haven't sold at the consigners, but that does limit the player's vault use). This has the benefit of being useful for resources and finished goods, as well as being in central locations (towns, player malls, etc.).
b) order silos - a silo which the player primes by placing one of the object they want to have the silo filled with, and sets a price per item with a max number of items. Again, cash is taken from the owner's account and put in an escrow for anyone who fills the order. Anyone can come by, check the silo for what it needs, and put in the requested resources. This is only good for resource gathering (helps miners and gatherers be viable business models) but it isn't centrally located so there is a drawback in terms of finding the work. This does avoid the possiblity of overstuffing though, and there is the marketplace channel for finished goods orders.