Explain the position of both. If other employees are present during the tour, briefly introduce them to the candidate. Some may ague that this may be misleading, but, if you explain the structure of the interview in the beginning, applicants will know that all candidates receive the same treatment. A tour is often the best way to give an applicant a feel for the job environment. When explaining the duties of the position, concentrate on the most important areas of the job and explain how the successful candidate will be spending most of his or her time.
Job descriptions tend to be vague in some areas.
Prospective employees are told to send a note thanking the employer for the interview, and the same courtesy should be extended to interviewees. I realize that librarians have very busy schedules, however, some kind of response within a reasonable period of time is only reasonable. I once received a note four months after an interview thanking me for my time and explaining that the position had been filled. If I were not a serious contender for the job, I should have gotten a rejection letter right away. A simple form letter would be fine.