A doubt is a gray area. Gray is something which is neither white nor black. Now, how to solve the doubt? An event, knowledge, convention cannot help. Then what can help? Accepting it either as black or white. Put it either as black and accept it or as white and accept it -- whether or not it is black or white. And see the gray as a shade of black or white. Either way you accept it. Honest or dishonest -- accept it. Then the mind is quiet. You are not in the gray area.
See, the eyes are dark, eyebrows are dark, and the thymus -- the most powerful organ of the body -- is black. Haemoglobin -- the main force of the body -- is black. You cannot survive without black. It is part of you.Or see it as white. Eye is also white. Bones are white; the structure on which the whole body stands is white.
Put your doubt in a category of black -- no problem -- accept. Put it in a category of white -- no problem -- doubt is not there. Have conviction, "I accept. They are dishonest and still part of me. That's it. Finished.