Always be impartial in your dealings.

Impartial : treating all rivals or disputants equally.Discourteous : showing rudeness and a lack of consideration for other people.Impudent : not showing due respect for another person; impertinent.Disrespectful : showing a lack of respect or courtesy; impolite.Unfair : not based on or behaving according to the principles of equality and justice.Antonym of Impartial is Unfair