Limit the game's number of core resources, alloys and alchemy, tools, items (weapons, etc), craft locations and services. Make all items basic items (upon crafting all stats are default) and use missions and challenges to add additional stats to tradables (to make them rare and worth trading). Create a mission builder that allows players to request services in exchange for tradables. For example if a player needs an Ice Sword to slay a fire dragon a smith could trade a special sword to the player(that will become the ice sword) in exchange for completing a frozen blade quest where the player would gain a frozen dragon tooth tool for the smith to turn X amount of swords into ice swords. If the trade post system always has NPCs making offers on player's needs and posting needs as well then the economy won't become stale. The quality of the game will directly correlate to the number of meaningful missions you are able to get into the game. Most importantly is to keep a paper rock scissors structure otherwise you will get trapped by linear leveling and players will quickly find the "end of the game". For example, paper that has all the possible stacked stats the game has to offer should at best draw against scissors but never win against it otherwise player's won't have a reason to go looking for scissors and the economy will go stale.
I would create 3 levels of services. Tactical services (engage target, access location, access item), Operational services (engage team, protect character, produce item) and Strategic services (engage dungeon, protect characters, produce items). The different levels of services enable higher level tradables to align with higher level services.
Let me know if this idea makes sense. It's inspired by the new Star Citizen game in production and its economy structure.