This is a fun question!
My ideal dive shop: First off, it would be clean, well-lit, and attractive, with some thought spent on carpet and paint and decoration, so that it's an inviting place to enter. (We have one shop here locally that has done a GREAT job with this.) That probably means a second entrance to bring tanks and gear in through, away from the retail sales part.
It would have inventory. This is one of the things that continually amazes me about dive shops -- Most don't have any, or very little. I know why -- Inventory costs money, both to acquire and to hold. But the single BIG advantage the retail shop has over on-line sales is the ability to touch and feel and try on merchandise, and if the shop has to order it, why on earth would I buy it from them at a substantial price penalty?
It would fill tanks promptly. And my IDEAL shop would have what my current shop has -- an "all you can eat" pricing for fills. I pay a set fee for a year's Nitrox, and I really, truly love that. And of course, my ideal shop would offer Nitrox and do helium fills, too. (And mine does.)
It would have a good service setup. That would include trained techs with some experience, and a clean, well-organized shop area.
It would have knowledgeable people behind the counter. When I ask a question about equipment, I'd like the person answering me to know more about it than I do
And getting realistic recommendations earns a shop BIG points in my book, especially if those realistic recommendations are not for the most expensive (most profitable) item in the store.
It would be run at least in part by divers. I say in part, because I think one of the big problems with dive shops is that they often ARE run by divers, who are not business people and don't have good business plans. But it's important to me that the people I interact with in the shop are divers, and know what I do and why I do it.
And the little stuff -- It would have someplace to sit. Divers like to hang and talk, especially while waiting for fills and such, and I have yet to be in a shop that had a bench or anyplace you could plant your rear end while waiting! I also like that my local shop usually has some kind of diving video running in the store. I can watch for thirty seconds, and sometimes learn something new. And most of all, people would be friendly. I
love the feeling of walking through the shop door (which I do several times a week!) and having somebody look up and look honestly pleased to see me (even if they aren't ).
I have yet to see a dive shop that has all of these things, although I know some which have several, and the shop I currently patronize has most.