In another place a rather arrogant non-diver insisted that all ***** (a particular agency, it doesn't matter which) dive shops are the same, that the courses are tightly prescribed so there's no difference between them whoever teaches them, so go for the cheapest. No amount of persuasion would sway his view - he clearly thought choosing who will teach you to dive is much the same as deciding where to buy your next packet of frozen peas.
While I would like to agree with Walter's oft stated view that the agency is far more important than the instructor, I'm afraid my experience is contrary to that. I was away from my dive center for a while some time ago and was relying on a particular instructor who had worked with me on and off for a few years. After I got back I discovered that he had certified someone as a PADI rescue diver after 2 days work and as divemaster during the remainder of his one week holiday. I fired him and told the agency of my misgivings - so far as I know they did nothing about what can only be regarded as bogus qualifications.
I also know that it is customary at some, maybe many, PADI diveshops for the CESA (controlled emergency swimming ascent) in open water to be performed without an upline. I was recently asked to teach an OW course for another dive shop, and when I asked about an upline I was told that they didn't have one and had never used one. This is stated by PADI as a serious breach of standards, but if those standards aren't enforced what value are they?
I have just completed the four dives for a PADI "referral" student who arrived with all class and confined water work signed off. I established that she had completed the knowledge reviews and exam verbally without ever writing anything down, and had only peremptorily or not at all performed the confined water skills. The "referral" course ended up being almost a full course.
Perhaps Walter has in mind that some agencies monitor their instructors more effectively than others, to ensure that agency standards are complied with? Because the fact is that actual teaching standards vary enormously within at least some agencies.