If your behaviour is free of deceit and untruthfullness, you are percieved as honest. Assessing if someones practicing honesty requires knowledge of truth.
It is important to note that incorrect facts, shared with sincerity do not constitute dishonest behaviour. That is behaviour that derives from genuine feelings, albeit potentially misguided.
Judging
Determining if someones behaviour is honest or not often derives from others personal judgement. This is not always simple and can involve assumptions, always a tricky practice.
In the famous parable about truthfullness, George Washington cut down a cherry tree and displayed the value of true honesty by admitting to it, when asked.
The tree was cut down, that is a fact. No one saw who did it so believing George to be truthfull is based on the assumption he would not lie about a misdeed.
I have no idea if George cut down the tree or not. Personally I cannot be sure he was not accepting the blame to protect someone else or even to establish a perception that he was a truthful person.
Proof and Evidence
Our judicial system is founded on the believe facts should be used to judge honesty. This is to avoid assigning dishonest behaviour arbitrarily.
Overall, there is no perfect way to judge a persons level of honesty, however, keeping an open mind and researching, validating and freely communicating your opinions are good practices to help avoid making erroneous judgements.
