That's not exactly true of all LFS. As someone who has worked in the pet industry and retail stores for a number of years, your argument is exactly what I would tell my customers when they wanted to buy something they didn;t need or shouldn't have. I would say " I am a salesman. I make my living by selling products. With that being the case, why would I be telling you NOT to buy something?" That usually got their attention.
But I also had the backing of the owners I worked for because they saw, with my ethics, they had more returning customers than 1 shot Sallys. But that also was during a time when fish keeping was a hobby mostly done by hobbyists.
Back when that 13 or 14 year old salesperson really was more knowledgeable than the customer.
That all being said, the pet business, as it is today, is mostly not run for the hobbyist but for the business man and as such, has to make profits. How much profit often determines the integrity of the store. This usually means hiring cheaper help and often unknowledgeable help. Unfortunately, I know a number of highly skilled hobbyists who opened fish stores only to fail because they were not good business people. But there are stores where good business and hobbyist like employees do exist. But how is a newbie to know which they are and where to go? Sadly, as earlier mentioned, it's usually after a bad experience in a shop and trial and error. A smart phone or the internet is not always the right answer as there are many sites with wrong or misleading information. Yes, you can look up where a particular fish originated from but what that site will probably not tell you is that what you are looking at in the store is not the wild version of the fish described and some or all of the information within will not apply to what you are looking at. THIS is where the knowledge of the store's employee makes or breaks a new customer or hobbyist. THIS is why it is important to notify the store's ownership that you won;t be buying from them because their salespeople are not qualified or knowledgeable enough or that their training regime is lacking in good information. Businesses need customers and when enough customers stop coming in, they will try to find out why and when enough people tell them why, they will either change or go out of business. It's that simple. I've said this before in other threads because I lived through it: The hobby changed when fish tanks became more about being a piece of furniture than the fish that were inside the tank. Little Johnny used to save his nickels & dimes to go to the LFS and buy some fish. Now, little Johnny has too many other distractions that cost more than nickels and dimes so in order to keep the business alive, stores needed to go after Johnny's Mom & Dad who had $$$$ to spend. That was then and this is now the fallout of that period in time.
I know this is a ramble but in a perfect world, only properly trained individuals would be selling things to properly qualified people. This is not a perfect world. It will only get better through your own actions. Stores go into and out of business every day. The good ones stay and the bad ones fail.... eventually. You become the deciding factor of a store's success. Big chain stores have their place but they should not be, IMO, the catch all for every pet. They have put many Mom & Pop shops out of business. Specialty stores can't exist if you compare their prices to the chain stores. They also can't exist if they have to meet those prices. So you can lay blame wherever you want but the bottom line is, if you want good service and satisfaction and someone to really care about YOUR success, YOU need to support them too.
Sorry for rambling but thanks for reading this.