Sick fish in a pet store...
I've said that a million times over - it's not that the pet store owners want to have sick fish. But if you know just a little bit of how this trade is run you will understand why YOU are quarantining the fish and not the fish store.
For smaller fish, that are in the range of $1.50 - $10 quarantining just doesn't make sense. It is the norm to have at least 30% of the fish imported from Asia DOA. They usually die in within 24 hours of arrival. The importers can request better packaging, less crowding etc. But I personally don't think anyone cares about the small fish.
I've received 200 Kuhli loaches in (I kid you not!) one quart of water! It was a stew, not fish swimming in water. After that we started to ask the exporters to bag certain number of fish in a bag and not more. Surprisingly no exporter resisted - they would do things exactly as you want them, no problem. The importer just needs to ask.
Back to the LFS. A LFS gets fish from an importer. The importer may care, but over time he will clearly see that quarantining fish puts him in a terrible disadvantage. Sooner or later one starts to think that it's all about moving fish. Import them, rebag them, send them out the next day if possible. Often the fish is pre-ordered - meaning as soon as they arrive in the US they are already bound to a store tank. They arrive on Monday and on Tuesday you walk in the store and see the fish. You never know that they just got in the US and are still stressed beyond belief.
What is important in all of this is to be aware of what I described before. The price of small fish is not big enough to justify quarantine. And keep in mind that a quarantine should be at least 2 weeks, and even better - a month. Many fish look fine the first week after arrival and develop issues only after that. That is the time when they are often in a hobbyist's tank already...
I'm posting this not to blame anyone. But to shed light on the logic and logistics of the small pet fish trade. The best practice is to buy fish from a store you trust. Know the owner. Know their practices.
--Nikolay