Not exactly the same, because there is no massive influx of new rupees. The rupees the buyer of the voucher pays were already in the game. Rupees are in the first place a tool for us to be able to trade in a convenient and cheap way and then a tool that can be used to hold value for some time. Holding value by hoarding of rupees instead of a set of items is bad for the ones who do that. For the economy it is potentially catalyst and multiplier for instability. If a significant part of the hoarders would decide to get rid of rupees that could create a big inflation and instability. Also, in a situation of a deflation like we have it now, the people might have more incentive to hold rupees in the expectation that the prices will fall. All in all, hoarding or rupees is not good. Yes, while the whole world is also already a single global market for many products and services. Plus tokens and, kind of, vouchers. Fees for locking the chests and SSS are a kind of taxation. Do moderators get some rupees, directly or indirectly? If yes, that would be kind of gov spending. We do have that as private agreements, not broadly advertised. The big difference is that we don't have civil nor commercial justice, we don't have civil nor commercial court. Not inflation but slight deflation. When due to an MC update the old stuff loses its usability (e.g. diamonds after mending and buying of armor and tools from villager came), the demand for that stuff drops, thus prices drop and the effect is some deflation - overall decrease in prices.
That shop has so high margin that it is easy to make a better shop - you just have to pay little more to the suppliers and charge little less the customers, there is plenty of room for that. Why only few people get this and run better shops? I'm not sure why that is the case, why there are only few who try to make good shops. Regarding monopoly, any attempt to corner the market and establish a monopoly can easily be fought against. All of the resources and all of the needed technology are rather easy to get. Yes, for example some people build a giant farm, run it for a month or two, get bored and go on to build the next farm. Bigger shops can at least partially compensate by buying stock when it is cheap and then slowly selling. Only shops with substantial capital can do that. I, for example, was too afraid of the inflation to ever hold a larger rupee balance. I don't think it is possible to safeguard against that, I'm even not sure if it is really a problem, if one should try to "solve" it. It is just a natural property of this game universe and we have to adapt.
