I must be lucky, my Petsmart has 2 very knowledgeable hobbiest and at least 1 is their most of the time. They have 180g sw coral tanks, outdoor ponds and fish rooms. They both belong to the local aquatic society also. My lfs on the other hand leaves much to be desired. The owner doesn't allow ill fish to be removed and quarantined and the plants also leave much to be desired. I have heard employees their tell of the 1" per gallon rule and when I spoke up about "I can keep an oscar in a 29g tank for life yet can only have 15 neons in a 15g tank" they were less than happy with me, lol.
Not that it matters to me, I made my point and know they are wrong in their thought.
The bottom line for me is research your fish yourself before you buy and trust no one with their input whether it be big box or LFS. At least until you have a good relationship with the outlet and know/trust those you are doing business with, and even then use caution and don't make an impulse purchase on anything you are unfamiliar with.