Other posts on centrism are here.
A moderate is one who takes two opposing positions and selects something in between. The opposing positions may be anything, so there are many people who call themselves moderate (or sometimes centrist). But moderation in this sense is dependent on the different positions one selects as the ends of a spectrum of positions. Thus anyone can call themselves a moderate.
A logical centrist is one who starts with positions that are contrary opposites, that is, they are opposites that pre-suppose one another. For example, one cannot have up without down, forward without backward, tall without short, etc., so these pairs are contrary opposites. Also included are functional contraries, such as libertarian and egalitarian, since generally speaking increasing one leads to decreasing the other.
Note that contrary opposites do not include the contradictory pairs true and false, good and evil, beautiful and ugly, etc. since they do not pre-suppose one another. That is, the true, the good, the beautiful, etc., stand on their own, whereas their contradictory opposites do not.
What is the contrary of a market economy? One says there is no market for something if either its demand is nil or its supply is nil. So, the contrary of a market economy is one without demand or supply. But that does not mean socialism, the state control of supply and demand, which is contradictory to a market economy.
A market economy tends to encourage greater demand and greater supply by stimulating demand through advertising and increasing production through capital investment. Its contrary opposite would encourage less demand and less supply by promoting conservation, frugality, and living simply. The centrist then selects something in between the contraries of an economy that encourages production and one that encourages conservation.