We on this forum probably consider ourselves as serious fish keepers, however I'm sure that for every member on here there is a person or two out there that see fish as a decoration or as an easy pet, and don't really take it as seriously as we do, and they're the ones that will buy from anywhere because they only have a basic understanding of the hobby, it's from these customers that the most money is made, a fish dies and they replace it, because they're cheap.
No store can rely on purely being knowledgeable in order to make money, there has to be a few white lies told in order to make money, store closures don't really happen unless the store specialises in other mammals, birds and reptiles also, amphibians not so much. Stores that specialise in fish, normally have a blind eye turned to them, especially the RSPCA, DEFRA may do something if some of the stock is illegally imported etc, but a few too many fish in a tank and they'll turn a blind eye.
People open fish stores with the intention of making money, giving advice comes second, unless you're a privately owned business, but still even some of them are bad, there are the odd few, but their turn over isn't as large compared to that of the other stores that will blag their way through in order to make a sale, it's good that some are honest, but realistically, the fish keeping hobby revolves around one thing...money.