Three sides to every story... His, hers, and the truth.
We all know that an LFS can give out bad advice at times, but on the other hand, if you want any advice, you need to ask the right questions.
When I go into an LFS to buy something, I usually don't want to play 20 questions with the store employees. It's not really their job to question me when I make a purchase, and I've actually only had one LFS ask me anything about my tank before selling me a fish. I feel like the one that DID question my tank (I was buying a difficult to keep fish), went above and beyond what they need to do as a retailer.
If I walk into a store and say:
"I have a tank at home and want to set up a freshwater tank. Where do I start?"
It's a much different scenario than walking in and saying:
"I just set up my tank and am putting in my first fish."
The first asks for advice, and should be responded to with proper information. The second is just chatting with the employee.
I don't know what happened here, and I'm not taking sides. I'm just pointing out that you want to educate yourself before walking into a store, and know what to ask.