They may all be very good, but some may be clearly better than all the rest. You must face the problem whether that difference is less important than the value of socially desirable factors in the appointment. A lot of people say that everyone is biased, therefore there is no such thing as objectivity, all evaluations are subjective and biased, and we cannot claim to be doing objective evaluations. True, all human beings are biased about something, but that doesn't mean that all human beings are biased about everything. And we can control bias to a considerable degree, e.g., the double blind design.
Ignorance is a great basis for avoiding being biased.
Then they may well have a preference for or commitment to some position on it. You may have very good reasons for your position. To prove bias you must show error or the tendency to error, not just the existence of preference. Otherwise all you have is their commitment to a position or a valid statement of personal preference. It may just be incompetence.