There may have been a time, long, long ago, when it was acceptable to just show up at the office of a perspective employer. The thinking is that a) it shows you’ve got moxy and b) it affords you the chance to get your face in front of the boss and prove how awesome and professional you are in person. That was then and this is now, so do not stage an interview ambush.
It’s safe to say that current interview etiquette dictates that even if you were in the running for a certain job based on your fantastic resume, exemplary creditials and astonishing talent and skills, popping in without an appointment will surely relegate you to the trash can file drawer. The thinking now is a) you don’t value the perspective employer’s time, b) you have boundry issues and c) you are out of touch with current business practices.
There is of course always an exception to the rule. You may consider the pop in strategy if you are in the restaurant or retail industries. That said, you’ll still want to do your homework and learn the slow times of day for the eatery or store. Also, arrive in professional attire, with copies of your resume in hand. Don’t overstay your welcome and don’t keep showing up, lest you be labled a stalker.
But again, unless you are in one of the two above industries, don’t call on them, let them call you.