I would say that blackmail is the intersection of {things that are indistinguishable from threats} and {things that are indistinguishable from trade}. And yes, from the perspective of the blackmailers that includes both some things that are trade and some that are threats.
It does, making ‘blackmail’ the wrong term to use when considering game theory scenarios. Some are ‘threats’, some are simply trade.
I would say that blackmail is the intersection of {things that are indistinguishable from threats} and {things that are indistinguishable from trade}. And yes, from the perspective of the blackmailers that includes both some things that are trade and some that are threats.