Spies are sent to earth, disguised as historians, to find earth’s weaknesses and strengths. Know thy enemy and all that, but they who know the past control the future.
To see what these people have done to each other... They are horrified at what they find. -- Anon Guest
So far, Terran colonies were the only civilisations interested in any kind of negotiations with Earth. And even then, those negotiations were lawsuits. Some of the bolder civilisations were starting to wonder why this was so. Therefore, they worked on special teams.
First - they had to be able to survive in the toughest of Terran environments. Which meant training with N'Ozzies, Inuit, and Mishmi sections of the greater Human Collective. They even got some additional wilderness training with some Crow descendants.
Second - they had to blend in. Humans could instinctively tell when something was wrong on such subtle levels that it was alarming. The more perfect the disguise, the more unnerving it was to humans who knew how humans looked and behaved. The Uncanny Valley met with Thin Slicing and synergised with any lingering xenophobia to create hostile reactions. Even in the Humans who were helping them.