This "advice" was not directed towards me, but is unfortunately typical of local Petsmart employee response nonetheless.
Customer 1: "I can keep these fish in my 10-gallon [apparently set up the day before] with the others?"
Petsmart Employee (bagging five four-inch bala sharks): "Sure. But they get pretty large."
Customer 1: "So, by then I should put them in a big tank - like forty gallons?"
Petsmart Employee: "Yeah, but they'll be happy in your aquarium for a while."
Customer 2 (approaching with a betta in a plastic cup of medicated water): "How long can I keep the fish in this?"
Petsmart Employee: "Oh...you can keep it in there for quite some time."
I'm kinda new at this so I don't have too much to complain about, but...
"Bettas don't like big tanks, they'd rather be in something really small since they're used to living in puddles..."
Also...
"1 betta and 3 zebra danios would be ok in a 2.5 gallon tank"
As he was putting some red cheek africans I traded them in a tank of Angels: "South American and African cichlids are all compatible."
Those same fish ended up in a tank of small Tang cichlids that were chased and beat up on constantly.
It's not quite advice, but....I was at Petsmart just today, taking a look at fish, and noticed that some of the Mickey Mouse platys weren't doing so well. A couple of them were sitting on the bottom, one nose down, barely moving their fins, one was gasping for air at the top and one was flashing at the gravel a bit. I pointed it out to the manager, and she stuck in the net to check the fish out...and the fish quickly moved away from the net. So she said, "oh, they're fine and healthy!" I predict they'll be dead within a day or two.