Have the actions that the players take effect overall economy. For example, if lots of objects are sold, shop keeper would be less willing to buy new objects, more willing to sell what they have. This could lead to a merchant type class (buy equipment from town where there is an excess, take it to a town where there is a shortage and make some money).
Some safeguards are needed so new players are not out of luck, have to prevent it from being too easy to get lots of money.
Balancing this will be fairly difficult, as within the game, there tends to be an excess of equipment to sell, and not enough equipment worth buying.
:Imho, there should be no gold in random monsters loot. Also, the metal equipment could be transformed into metal bars by some npc'sm who would be buying it then. Now, the use for metal bars should be found. This could be applied to any unusable loot - organics could b bought by alchemist, who transforms them into buyable potions. NPC's could trade between themselves then. Half of shops would be4 people buying materials, and they would be selling they're production to shops. This would make players check if prizes of some materials aren't raising, before going on looting trip. – kshinji
::Just noting that in the mlab maps (citydeclouds) there is a small area that makes use of ores and metal bars (refining them into bars, then exchanging them for swords, etc). However these maps are beyond what has been committed to svn(then cvs) of mlab. Keep in mind that more political issues would result from committing those remaining maps to svn.