With few exceptions—Bernie may be one—I'd say it's extremely hard to tell how much of a politician's positions reflect their "authentic" personal beliefs vs. things they say "to get elected". So when people try to make those distinctions, your BS detectors should be set to high.
Furthermore, quite often the notion of "authenticity" has been wielded in a way to make it harder for women and people of color to get elected, e.g. they're described as too ambitious or not true to themselves. That's another reason to be wary of it.
Finally, it's not obvious that it's preferable in a representative democracy to have a politician who sticks to his or her personal beliefs at all times. Nor do you want someone who's always flip-flopping. But you probably do want some responsiveness to one's constituents.
