If you reasonably ought to have known that the sky is blue, but didn't
and thought it was green, and said so, when, if ever, would lawyers
consider that dishonest?
One of the concepts that is widely used and most extreme involves cases of "willful blindness" in which the person deliberately refrains from obtaining information he or she should reasonable know in order to lack actual knowledge of it, even though the person who is being willfully blind believes that the information in question is something that he or she would be at a disadvantage if he or she actually knew.
So, if you believe fraud is probably occurring, but make a point of never examining the facts you would need to examine to be sure, you are being willfully blind and that is a form of dishonesty.