I was probably imprecise in my language earlier, referring to money and coin, when I should have described it as "value". There are actually two concepts that are related but different, "value" and "liquidity". Value is like GDP for a country -- the total value (as determined by the loot tables) of all the drops in the server. The second is liquidity -- most of the loot has to be liquidated in order to have a useful economy (a pure barter economy would be grossly inefficient), and NPC merchants allow you to exchange value for liquidity at a pennies-on-the-dollar exchange rate. Liquidity is effectively the cash money supply available at any given moment. Since the overall cash money supply is dependent entirely on the value (GDP) that the server is generating, but constantly tracking the money supply is not easy, efficient or necessarily effective, tracking the value generated by the server (all inputs) and all the value being taken out of the server permanently via gold sinks (all outputs) ought to be an easier task.
I caution that drawing any parallels to "real" economies is going to break down at a certain point when you are dealing with artificial, virtual game economies, because they do not have the same market forces acting on them (except in the most rudimentary ways) and don't have the same market correction mechanisms that a real market has. For example, in real life if a money supply is growing too large, the price of money (i.e. interest rates) falls and it spurs more borrowing and lending, and more consumption. However, POTM has no mechanism for lending or interest rates to respond to increases in liquidity, nor does it have a federal reserve bank to tinker with interest rates. As a consequence, we cannot simply act as if this is a "free market" and let things roll however wild the ride. Nevertheless, I am not an advocate of blunt force trauma to correct perceived market disruptions -- I think the optimal way to control a game economy from rampant inflation or deflation is to simply balance inputs (loot drop value) to outputs (gold sinks). There will need to be some margin in favor of gold sinks, simply because even though value is exchanged for liquidity at a discount by NPC merchants (i.e. they buy low and sell high), a lot of loot drops are not recycled back to the community at a higher price and therefore are not effective gold sinks (see my thoughts below for a more thorough explanation of this). Thus, the outputs have to be larger than the inputs to account for this. It will take some tinkering to sort out exactly where the balancing point would optimally be.
Another factor to consider is to avoid loot drops that are effectively "junk" (i.e. they get exchanged for liquidity, but will never be purchased by the player base). Tarnished wedding bands and similar ilk are an example of loot that will only be sold and never purchased, thus increasing liquidity but not functioning as a gold sink in return. Loot that has a purpose and value that would incline other players to want to purchase it (even at a higher price), thereby taking liquidity out of the system, is preferable to loot that is merely sold and has no life beyond that. Consumables are usually a preferred option (especially if they were made stackable and thereby more easy to carry and quickslot), but I recognize there are a lot of "flavor" loot drops that people might play with for novelty before discarding.
I will note also that while some consumables (oil of conquering glory and similar) have a value and may be wanted by lower levels to augment their limited casting abilities, they are often simply disposed of with NPC merchants so that gold can be split by groups, and repurchasing can be expensive for the low levels that actually could use it (and the fact that many are one-shot or limited shot consumables that don't stack is an inconvenience).