I wonder if this would be a viable mini-business in Puzzle Pirates:
The "system" (aka the man) charges you a 10% or so fee to transfer your poe between islands. This fee goes up if you want to transfer between islands in different archipelegos.
Could a player or group of players who have significant idle holdings undercut this practice?
The problem is that the poe needs to get there. Either via an able crew, or just general accumulation, let's say for the sake of argument that the poe is at several locations arleady.
One could create a website (that is updated -- the not fun part) that knows how much poe is where. Users can enter the place their poe is and where they want it to go. The system will then tell them how much they can transfer (the lower of the poe onhand at those two destinations), and the fee.
The player would then have to arrange a time to meet with a trusted broker to close the deal.
Building trust is obviously an issue, as the broker cannot trust the customer. Ingame events like auctions and such should be enough to get the ball rolling. False accusations of fraud from dishonest players will be a problem, especially if they occur while the system is getting started.
It may be that the majority of transactions serve to centralize the poe, or worse, decentralize it to where it is scattered and not useful. Talented sailors will then have to be enlisted. Perhaps the sailors could be commissioned, without the need to trust them implicitly. If there exists a general trust in the organiztion, it could itself advertise for "poe delivery", paying a percentage on the income, perhaps at either isle. This percentage would need to be at least 5% lower than the 'transaction rate' charged to customers.
Scale is a problem, as a system of trust would need to be created among the brokers. However, once established, brokers could operate as independant agents to a large degree. They can maintain their own network of poe, post their own bounties for poe deliveries, etc. Indeed, they must maintain their own poe, as no-one can be trusted with the "communal pool". To this end, they will need to make their own deliveries. If agents are competing with each other to make transactions, this will tend to ensure that deliveries are as timely as possible.
Trust could be "ensured" by requiring new agents to provide a "Security Deposit". Agents are then allowed to make transactions up to their security deposit. This provision could be removed for longtime agents. Dishonest players, however, can abuse agents by falsely reporting fraud (certain to happen). This will be indistinguishable from actual fraud.
Agents would be easier to trust if the poe were paid to a central system rather than the agent himself. Perhaps deposits on private sloops or somesuch can be arranged. This would necessitate an investment of purchasing sloops for each new 'source'. Except that doesn't help at all. Dishonest agents can simply falsely report delivery of the poe and collect the replacement payment and their fee.
Is there any way for the agent to "prove" the transaction took place? Screenshots can be faked, chatlogs are laughable. Banking data is private. Perhaps ships can again be helpful? Their transaction logs can show who took the poe and how much, though poe can only be removed by crewmembers. A pirate may only be in one crew at a time, and the customer may not have the ability to add the Agent, nor the inclination to leave his crew to receive his shipment.
These troubles would be acceptable for large amounts (10k+ perhaps), and perhaps the risks are minor enough to dispense with these precautions for smaller amounts.
This entire idea could be expanded to any type of commodity, actually. Storage of anything but poe is difficult, however.