user-1: A common belief is that, if one conducts himself "as best he can" (in the best ways he understands and knows), then would be a protection from -- or an excuse for -- wrong-doing.
For example, "I answer with best effort and understanding..."
Under the context of truth, the Dhamma, is this just a naive thought of foolish people? Or can such be rightly justified as something an Awakened would approve?
[Not at all given for trade or keep people caught in corruption]

user-1: I cannot see how it would be possible to do any better than doing the best we can. If we do this but inadvertently cause suffering or harm then it would hardly be fair if this created bad karma. 
Surely it is intention that matters, not the outcome of the action, especially since approximately all the outcomes of our actions cannot be known in advance.  
The only proviso seem to be that 'doing the best we can' must involve the acquisition of knowledge, since ignorance is no excuse for wrong-doing where it is a choice.     

user16855: Doing the best one can is relative to what one knows. If what you know is the method described in the Dhamma, then 'doing the best you know how at the time', if followed-up with a little review of the results will move you steadily from higher to higher and on out.

user471: Doing the best that you can, is not a protection against wrong-doing.
Why? Ignorance, or the lack of Right View and wisdom, may cause you to commit wrong-doing, despite doing "the best that you can".
Hence, gaining Right View, and gradually improving Right View and wisdom over time, through insight, will push the boundaries of your "best effort".
In the Salt Crystal Sutta (translated by Thanissaro Bhikkhu), the Buddha taught:

'Now, a trifling evil act done by what sort of individual is
  experienced in the here & now, and for the most part barely appears
  for a moment? There is the case where a certain individual is
  developed in the body, developed in virtue, developed in mind [i.e.,
  painful feelings cannot invade the mind and stay there], developed in
  discernment: unrestricted, large-hearted, dwelling with the
  immeasurable. A trifling evil act done by this sort of individual is
  experienced in the here & now, and for the most part barely appears
  for a moment.

And there you have it. For protection from wrong-doing, one should be developed in body, developed in virtue, developed in mind, developed in discernment and dwelling in the immeasurable.
The same paragraph translated by Bhikkhu Sujato here:

What kind of person does the same trivial bad deed, but experiences it
  in the present life, without even a bit left over, not to speak of a
  lot? A person who has developed their physical endurance, ethics,
  mind, and wisdom. They’re not small-minded, but are big-hearted,
  living without limits. That kind of person does the same trivial bad
  deed, but experiences it in the present life, without even a bit left
  over, not to speak of a lot.


-1: <p>A common belief is that, if one conducts himself "as best he can" (in the best ways he understands and knows), then would be a protection from -- or an excuse for -- wrong-doing.</p>

<p>For example, "I answer with best effort and understanding..."</p>

<p>Under the context of truth, the Dhamma, is this just a naive thought of foolish people? Or can such be rightly justified as something an Awakened would approve?</p>

<p><em>[Not at all given for trade or keep people caught in corruption]</em></p>
 -1: <p>I cannot see how it would be possible to do any better than doing the best we can. If we do this but inadvertently cause suffering or harm then it would hardly be fair if this created bad karma. </p>

<p>Surely it is intention that matters, not the outcome of the action, especially since approximately all the outcomes of our actions cannot be known in advance.  </p>

<p>The only proviso seem to be that 'doing the best we can' must involve the acquisition of knowledge, since ignorance is no excuse for wrong-doing where it is a choice.     </p>
 16855: <p><strong>Doing the best one can is relative to what one knows.</strong> If what you know is the method described in the Dhamma, then 'doing the best you know how at the time', if followed-up with a little review of the results will move you steadily from higher to higher and on out.</p>
 471: <p>Doing the best that you can, is not a protection against wrong-doing.</p>

<p>Why? Ignorance, or the lack of Right View and wisdom, may cause you to commit wrong-doing, despite doing "the best that you can".</p>

<p>Hence, gaining Right View, and gradually improving Right View and wisdom over time, through insight, will push the boundaries of your "best effort".</p>

<p>In the <a href="https://www.accesstoinsight.org/tipitaka/an/an03/an03.099.than.html" rel="nofollow noreferrer">Salt Crystal Sutta</a> (translated by Thanissaro Bhikkhu), the Buddha taught:</p>

<blockquote>
  <p>'Now, a trifling evil act done by what sort of individual is
  experienced in the here &amp; now, and for the most part barely appears
  for a moment? There is the case where a certain individual is
  developed in the body, developed in virtue, developed in mind [i.e.,
  painful feelings cannot invade the mind and stay there], developed in
  discernment: unrestricted, large-hearted, dwelling with the
  immeasurable. A trifling evil act done by this sort of individual is
  experienced in the here &amp; now, and for the most part barely appears
  for a moment.</p>
</blockquote>

<p>And there you have it. For protection from wrong-doing, one should be developed in body, developed in virtue, developed in mind, <a href="https://buddhism.stackexchange.com/q/26224/471">developed in discernment</a> and dwelling in the immeasurable.</p>

<p>The same paragraph translated by Bhikkhu Sujato <a href="https://suttacentral.net/an3.100/en/sujato" rel="nofollow noreferrer">here</a>:</p>

<blockquote>
  <p>What kind of person does the same trivial bad deed, but experiences it
  in the present life, without even a bit left over, not to speak of a
  lot? A person who has developed their physical endurance, ethics,
  mind, and wisdom. They’re not small-minded, but are big-hearted,
  living without limits. That kind of person does the same trivial bad
  deed, but experiences it in the present life, without even a bit left
  over, not to speak of a lot.</p>
</blockquote>
