Harvest of Deed
The Guilds deal with each other using a currency called ‘Deed’. Every single favor between guilds has a Deed cost attached to it. For example if the Guild of Swords requires a Wizard for a mission they would pay 100 Deed to the Guild of Magic for a level 10 Wizard to assist them. Deed is organised by a veritable army of bureaucrats who keep track. Deed is passed via lacquered wooden coins, ornate scrolls with a large seal, or as masterwork items crafted for the purpose. Particularly special Deed will earn miniature seals or scrolls that can be attached to armour or weapons as a permanent record.
This Deed system is rumoured to have come about after rulers of the kingdoms began to realise the guilds had more power than the rulers themselves. The story goes the rulers instigated the system under the ruse that they wanted to make sure every guild was treated fairly and would not rule over another.
The kingdoms themselves trade supplies and tradesmen to the guilds in return for Deed, and a King has the right to grant Deed to a guild in return for their services. The law always reinforces the idea the citizens power is the same as the king as they buy service from the Guilds in the same way. The way the bureaucrats say it:
Coin is between the Citizens and their King, Deed is between the Guilds and their Masters.