I had what I'm going to call a semi similar encounter at my LFS a few weeks ago. Luckily it was an entirely different outcome.
I was talking with the owner of my LFS as we have become pretty well acquainted, when a mother and two younger children had came in and started to look around. The owner, obviously asked if there was something that he could help them with. The mother started asking questions about snails, how much they were, what type was the best, ect. Usually a pretty normal questions for someone looking to add a few snails to their tank but the questions were really vague. So the owner asked, how big of an aquarium do you have? That's when the mother informed him that they were just looking to start a small tank because the daughter wanted a snail.
Long story short, the owner of my LFS quickly and simply explained the basic fundamentals of cycling a tank, why we cycle a tank, and then proceeded to explain that if she was simply after a snail, its going to cost a lot more than just a snail and some salt to keep it alive. He said, he can't sell her a snail, but he would gladly help them get everything they need to get setup to keep a snail and possibly a few small fish. The mother was very understanding and quite clearly in shock that a snail would cost a few hundred dollars when it was all said and done. LOL she said that they have a lot of learning to do before they commit to such a large decision.
Now that is how I can only hope every conversation of the uninformed would go. Unfortunately though, do to our society's need of instant gratification, I picture most of these conversations going the route of OP's encounter. I do know though, that the owner of my LFS will never sell a fish or coral to a customer without knowing their tank setup. To him it doesn't matter if people think of him as an A** or rude, or arrogant. That's just one of the many reasons I will always support him. Not for his love of the hobby, but for his love of the animals that we keep for our amusement. I will admit that sometimes I don't agree with him, but his 40+ years of experience with the ocean and 30+ years of studying the ocean on an academic level remind me that I'm new to this hobby compared to him and whether or not I like what he is saying, he is saying those things for a reason. He's a professional, I will always heed his word over those like the team at BRS or some of our fellow members here. I just wish more people would see it like that when shopping at their LFS, whether they are new to the hobby or not.