Lfs used to run qts in their stores, you could not even bribe them to sell you a fish until it has passed. An lfs would ask you about your setup and tankmates and refuse to sell you a fish that would not work in your environment. If seen an lfs refuse to sell to customers all together when they observed negligent behavior. A lfs would agonize over every sick or dead fish. Lfs would not even carry fish that had such a huge mortality rate that their chances were slim.
Now let's fast forward to today. I see the same lfs get an order or 125 fish, over half of them dead in a bucket within a day aor two; no problem do it again in a couple of weeks. Lfs do not even care your setup or who's in the tank; I've overheard some of the most absurd advice and sales pitches to get the customer out the door with a fish. I've stopped customers from making huge mistakes, like putting a volitan lion in a 50g with small gobies and cryptic wrasses. Nano reef being sold huge blue sponges and sea apples that eventually wipe out their entire reefs. This is so rampant I could hardly even cover even 1% of what I've seen. I started a dwarf lion rescue tank after an owner of lfs that didn't know me give me a sales pitch on a pale dying fuzzy dwarf and telling me he was even eating flake food with gusto. After tracking nearly 20 dwarf lions over the last 3 years, only one lived more than a year; more than half died in the store. I watched lfs pass these guys on to customers that had no idea how to handle their feeding requirements. Disease is absolutely so rampant, there are 2 lfs in town that absolutely nothing they sell lives. I could go on and on...........Beginning hobbyist still rely on their lfs for support and advice; some don't realize that the internet is full of experts. But it still doesn't change the source and the route these fish travel.