So what is the lesson here? I hear this saying over and over, always with the implication of "Give them a pass". Who cares if they are being crooked, or are too dumb to do division. Either way, the employee loses.
Given my experience of advising early stage startup founders on equity investment, dilution, cap tables, etc., I believe that ignorance is at least as likely as malice in situations where they seem unwilling to disclose all the information the potential employee needs to fully evaluate the potential value of any equity options being offered.
I would never join a startup where the founder wasn't razor sharp and forthcoming on all these details.