And instead of the experts at the local fish store I'm supposed to trust complete strangers online who I have no idea who they are, how old they are, how experienced they are with fish, etc, etc, etc. ???
Welcome to TFF!
I'm John, 52 years young, my tanks & such are in my profile, as is my location. They tell me I'm supposed to do stuff around this forum, I usually do, when I'm not messing with my tanks, 3 dogs, or old trucks. I work full time in the printing industry, most often as a pressman.
I mostly breed NW cichlids when I have the time, angels in particular. I sell a variety of items on the side, blackworms, dry food, along with fish. When life gets too busy for breeding I'll get fish in, looking at getting 300-500 angels in this week, besides assorted other species from a much larger breeder. I sell fish to shops, I might sell to the second shop you mentioned, I would not sell to the first, I'm very selective in this respect. I'll get in 25-40 pounds of worms, 20 pounds of dry food, and turn it around in a matter of weeks, the fish might take a month or so.
I've held various exec, board and committee positions in my local aquarist society, have written and enacted various programs, put on various presentations, run various events, and so forth. I'm a regular vendor at many club related events around the Midwest, often contacted & requested to be a vendor at these events.
So I guess I'm not a complete stranger any more!
In my mind a professional is someone who makes the majority of their living at that profession, so I guess I'm not a professional. The guy selling burgers at McDonalds probably does, so I guess you could call him a professional. The sales staff at most local fish shops are a step above burger guy, but all too often not a very big step.
An expert to me is someone the professionals go to when they need advice, have a situation they can't solve, and so forth. I've had shops ask me for help when they've been in a jam; I don't consider myself an expert by any means. In aquatics an expert will most often cover a very narrow, limited portion of aquatics, but will do it extremely well.
All this being said, the folks here are steering you in the right direction, regardless of what you are told by shops, who's main interest is moving product & showing a profit. General aquatics books are often dated, newer information arises which is often not added in a revised edition.
Your best chance of getting current general aquatics information is a forum such as this, as so many situations in more areas of the world than I know of are represented, far more than any shop or author of a book will experience.