If one player wanted to hire another player as a mercenary for pay, how would this work by the rules? What is the mercenary required to do to show he is a mercenary, how much is he allowed to be payed and how do we announce the arrangement on the forums if it is even necessary? I am iffey on how the whole trading / payment thing works... :/ thanks.

If it's a merc for a war, he needs to declare it on the war thread and the alliance leader needs to confirm it.
Payments in resources should not violate the pushing rule. You can also use rubies. (there are no restrictions on rubies)

so...how does being a merc / having a merc work? Can't you just have a mercenary to attack another planet but "not get your hands dirty" or something of that sort?

Sorry, I'm new to all this lol

As long as res payment does not violate the Pushing rule then yes. You may hire another player to hit a colony or even do a MD.

just put the resources on the moon with no defense and let the attack you, you will be within the pushing rule. ohh and be sure to buy tons of rubies just so you get screened of as a ruby buyer from suspicion.