Mmmm ...
The advice given above are very valid ...
The point is the appearance of an applicant goes to how he/she rates themselves ... if you appear dishevelled or imprecise in anyway at an aviation interview it worries the interviewer that you 'may' be imprecise in other things as well (such as mental process & decision making) ... and as helicopter aviation is not very tolerant of mistakes, the interviewer likewise will err on the side of safety in his selection criteria.
It may seem unfair ... but that is usually the way it goes in real life.
Good luck ...