I say I have nothing to gain, nor lose from telling you the 'truth', because if I wrote a book about the military for 'free', this would mean I considered the military a hobby, or I wanted you to join, or I wanted you not to join, therefore, it would be bias.
Because the book isn't free is evidence of its truthful authenticity.
I don't care if you join, I don't care if you decide not to join.
What I do care about is telling you the 'truth'.
I hope you understand where I am coming from now.