A battle mine can put a merchant on a host battlemine that is visible. merchants makes the host able to see trades offered by the merchant owner via global trade even if the merchant owner is not visible or in another part of the map. merchant costs to hire depends on what you mine. 1 EUR for uranium miners, 2 alum for bauxite miners etc the host battle mine can remove merchants on its land by paying the amount to hire a merchant , 1 EUR for uranium miners, 2 alum for bauxite miners etc
A central marketplace where you can post up trades and set resources in escrow (Sorta like FFXI style) would be a large step forward in increasing the interactivity of BM - lately it has become a bunch of separated factions with little to no socialization between them.