When you are interviewing au pair candidates, you need to be certain that the level of English is good enough for you to communicate. It is normally easier to communicate in person than on the phone, but don’t assume that it will be. Be sure that you could deal with the au pair’s level of English if she arrived and it was exactly as it was on the phone.
Keep in mind that the interviewer who is evaluating the au pair’s English proficiency is probably not a native English speaker. Therefore, his or her idea of good may not match up with yours.