If a shop will not let you interview the instructor you are going to have- find another shop. That is complete and total bull crap. The first thing to remember is that when you sign up for classes, as the consumer you have the final say over who teaches you. Or you can, and perhaps should, take your money elsewhere.
This is one of the reasons I put an entire chapter in my book on choosing an instructor and one on choosing a shop. What you are actually doing when you sign up for classes is HIRING someone to teach you how to dive. You are, in effect, hiring an employee. New divers need to have this in their mind when signing up for a class. I don't take a cent from anyone until they have had a chance to interview me personally.
You have to ask why would a shop not allow you to interview the person you are trusting with your life and maybe that of your family? That person is the one who is going to minimize the risk to your safety, security, and perhaps financial stability by teaching you how not to get hurt or worse underwater. Why can't you talk to them? They can show up for a class right? They can show up early or stay over to talk to a new potential student.
When you fill out that paperwork and hand over the check, cash, or credit card they now work for you. Not for the shop. If they don't have that view - RUN AWAY!
Jim, I'm sorry, but I think I have to disagree with you on this. I do absolutely agree that the individual instructor can make a difference, but you have to be reasonably practical here. I am one of a bunch of instructors associated with the shop with which I work. I just got my spring schedule earlier today. If someone wants to interview me to see if I am good enough to teach the class that is scheduled on the time slot when they want to take the class, how are they going to do that? I will be in Florida for two months prior to my first scheduled class. Am I supposed to fly back to Colorado to meet a prospective student to see if that student, in his or her infinite wisdom and ability to discern instructor competence, deems me competent enough to teach the most basic class in scuba instruction? Even if I am in town, do you really think anything valuable is going to happen? Do you really think that this student has the ability to choose the instructor so well that he or she is going to make an intelligent choice? Is the shop management going to call all the instructors for this shop in for a lineup so that this discerning student can select the best of the lot, like some sort of a bizarre Miss Universe contest? It's not going to happen, and calling for students to do something like that is like calling for them to find a unicorn.