Due to the fact the Academy really doesn't give a lot of details about the role of the BGO interview, there are some honest misconceptions. The BGO is not a candidate's friend, advocate, coach, mentor, or the man/woman in your corner. The BGO does steer the candidate in the right direction and gives advice on how to make themselves the most competitive. The BGO makes sure the candidate knows what they are getting into with regards to both the Academy AND the Navy. The BGO makes himself/herself available to answer questions about USNA and the Navy and any problems the candidate may be having with the process. Finally, the BGO interviews the candidate ON BEHALF OF THE NAVY not on behalf of the candidate. Notice none of this involves a close personal relationship with the candidate---the BGO is as neutral as an interviewer for Microsoft. This is a shock to some candidates who think the BGO is supposed to "help" them. I will also admit that there are some BGOs that violate all of what I have described and do their own thing.....that's one of the downsides of dealing with volunteers.
For the interview, the BGO has a number of items he/she must comment on based on their admittedly limited viewpoint like leadership, responsibility, motivation, etc. On each of these areas, the BGO rates the candidate such as average, top 25%, below average, etc. Then based on those separate evaluations, the candidate gets an overall rating. Again: average, top 5%, above average etc. Finally, the BGO can express their gut feelings. The BGO lastly either recommends or not recommends the candidate and his recommendation had better match his prior ratings. Very few candidates get a "no recommendation" as we are dealing with some top kids here. Going along with that, every candidate's interview goes great from the candidates view---why shouldn't it? What counts is the relative standings of different areas which add up to the overall recommendation which in turn is compared against the candidates competition. I always tell my candidates at the end of the interview that they are a great candidate and good luck to them. It is always the truth too.
All of this background info is great but totally irrelevant to the individual candidate as they can't influence any of it. A candidate prepares, does the best he or she can, lets the chips fall where they may and flushes the agonizing from their head.
Much more on the role of the BGO and their work can be found in the superb book "The Naval Academy Candidate Handbook" by S.Ross available for $20 on Amazon.