We all know that Luffy doesn't work for anyone , right?
So , lets put it like this: what if the marines ask for luffy and luffy's crew to be a shichibukai ? And his reward was meat ... do you think that he would accept it? You guys know how luffy is ^^ like for example... every mission accomplished the marines would sent him meat as a prize ... xD.
just for talk ^^ (we all know that he wouldn't work for anyone xD).