There was an online discussion about Gold Selling and this is what I came up with.
Every citizen will have to pay taxes to be citizens of a node, whether they live in a tavern, or a freehold. That is a gold sink, and need not be fixed price. As the value of that node citizenship goes up, so can the tax rate.
Membership can be variable, and so is therefore the gold sink variable. All I have to do is set the total tax payable, to be equal to the gold value of everything produced, or farmed in that node, (whether it is by members of the node or not), and I have a zero sum economy, by definition. This can kick in only at say Level 3/4. (Might be good to set a variable here for balance).
This might be a genuine solution. First of all if the tax scales by node citizenship as well, it limits the population of a node and therefore zerg guilds/nodes/factions.
Secondly, it creates a method whereby a node that is popular, even to non-citizens, it will collapse under its own weight, so that the citizens can't afford their taxes. You create a natural mechanic by which nodes can collapse, and you have an unlimited end game. Also a system of PvE economic warfare.
It would also provide a PvP guild/Node with an incentive to play defense, keeping non-citizens out, lest they destroy the economy of their node. And therefore a natural curb on gold selling. If you farm gold from a node, and then sell it, rather than appreciating the goods you sold, by processing/crafting, then the node will collapse economically. The gold sellers become persona non grata in every node, and/or can't be citizens in the node if they don't use the gold to pay their taxes. They might as well be NPC bandits, and part of the game either way. You might be able to sell/gift a bit of gold out, enough to help a friend/relative, but no one is going to make a living out of it.
Maybe my A-Level high-school economics is flawed here, but I can't see any economic problem, and you get a stable (pseudo) zero sum economy.