Something I learned is the LFS doesn't really care. They need to make money so will tell you what they need to tell you to make money. They may have good intentions behind their advice, but they are almost always in a grey area of "in perferct circumstances and with luck you could keep this fish."
Unfortunately you 100% have to know what you are doing when you walk into a store in this hobby. It's hard because you walk in with knowledge of fish x but they only fish y and you really like fish y. Take 10 mins to look it up on your phone and go from there. I'm telling you, this will reveal the LFS blowing smoke most of the time. Again they probably aren't trying to screw you, but they have a job to do and can't personally review everyone's tank every customer.
Case in point, when I was brand new my LFS sold me a blue tang for a 20 long. Told them I was new and my tank was 3 days old. Obviously it died that night. Went back to the store and THE SAME GIRL told me my tank was too small and too new. I rarely go back now except for CUC. If you are in North Houston, I'm talking about fish gallery.