Everybody, included so an interviewer, are impressed, at first time, by the appearance. The reason, in my opinion, is because our society is conditioned by images. We judge people, at first, because he or she looks like.
After that, probably, the qualities most important for an interviewer could be, following this order: experience, qualification and personality.
The background of a person is important if you need an experienced worker, and –in my opinion- personality couldn’t be reached in only one or two interview. Although psychology could help you to describe a human characteristic, there’s only for a specific time and I think personality can change in a little time.