I'm not familiar with the associated ancient Greek word for middleman (-poly and -psony come from ancient Greek), but in modern Greek "μεσαζοντας" (pronounced m

I'm not familiar with the associated ancient Greek word for middleman (-poly and -psony come from ancient Greek), but in modern Greek "μεσαζοντας" (pronounced meh-sa-zon-das) is "middleman". So that would suggest something like "monomesazontia". There is also "μεσίτης" (meh-see-tees) which means broker / facilitator. That would suggest "monomesitia". But if you're willing to mix Greek prefixes with English/Germanic roots for "dealer", then I like the sound of "monomongery" :)