In other words, how do I know if I'm really being objective?
How to avoid subtle biases and inclinations to influence phenomena when doing vipassana?
Find out the difference between what are concepts and what is.
Follow the sensation of the breath not the idea of the breath.
Follow the sensation of the feet as they move exactly in the present moment and don't follow the idea of the feet.
Notice thoughts as they happen or as they are remembered but don't make an effort to notice or not notice the content of the thoughts.
Notice what mental content is being reacted to, notice intentions.
When you merely witness what is in attention and realize that it is what it is then there cannot be any bias in that moment. Bias comes with consepts.
One of the most powerful and useful suttas is SN12.23 Dependent Origination.. SN12.23 lists the things you can observe while being rightfully mindful of biases and inclinations. For example, suppose a seductive thought comes to mind. Then one can use this sutta to find the roots of that craving:
I say that craving has a vital condition.
And what is it? You should say: ‘Feeling.’ … You should say: ‘Contact.’ … You should say: ‘The six sense fields.’ … You should say: ‘Name and form.’ … You should say: ‘Consciousness.’ … You should say: ‘Choices.’ … I say that choices have a vital condition, they don’t lack a vital condition. And what is the vital condition for choices? You should say: ‘Ignorance.’
One can look for and relinquish the feeling (e.g., "there was attraction" vs "I liked")
One can look for and relinquish the contact (e.g., "there was a sight" vs. "I saw")
One can look for and relinquish the six sense fields (e.g., "there was a sight" vs. "I saw softly billowing hair in the sunny breeze")
One can look for and relinquish the name and form (e.g., "healthy person" vs "beautiful blonde")
In other words, use the the efforts to restrain, to give up, to develop, and to preserve
By not trying to avoid them .You let it all come, your very avoidance is recognized ,there is no certain state that needs to be achieved,because if you put that in your mind then always you will need to get to that state else you feel disconnected and thats called rapture .
The play of life is happening and at emptiness there is looking without a looker ,no conceptual understanding is forced ,the play is simply happening with all its colors .In Vipassana there is realization of that which is already happening no special state needs achievement no miracle ,just realization of the miracle that is already there ,when that realization is perfectly clear and not just a flash ,there is a new rooting in the emptiness instead of the identity and no need for methods.