Be careful what you wish for. One thing to remember is that if people aren't trained to do a job, how can we expect them to do it properly? The burden there lays on the store and management. Another thing to remember is that "store policy" has a lot to do with how the staff treats the animals as for basic care. There is a LFS not far from me who's owner and manager don't feel the need to feed the fish, claiming they shouldn't be there long enough to need food. These same 2 men also claim that water exchanges are also unimportant for the store tanks. The only thing either of them sees in their job is a chance to make a quick buck. When a staff member approaches management or even an owner about these issues, it's not always received with open arms. A friend of mine quit working at this store because of their practices and beliefs. She went to work one day and heard the general manager telling a customer that bettas breathe and blow bubbles via a hole in the top of the head, like a dolphin or whale. When she approached him, he was vulgar with her, and ordered her to "get back to work". When she approached the owner, he laughed at her, told her it didn't matter. My friend was told that her job was on the line if she medicated the sick fish, planted the tanks with live plants, or did other "maintenance" to the tanks other than just selling the fish. When she finally witnessed the general manager put an entire shipment of mudskippers into a full freshwater tank, like fish, and killed them all in 24 hrs, she'd had enough and gave her notice.
Unfortunately, these are the horrors at many pet stores... lack of education and lack of humanity are the 2 big causes.
When buying fish, NEVER put their water into your tank. In places like described further in the thread have systems running all together like that, ask what the water parameters are... they probably don't even know. Many times these systems are overloaded in ammonia, nitrite, and nitrate. This is not water you want going into your healthy tank at home.
When shopping anywhere with an enclosed system, 1 sick fish anywhere in the system means all of the other fish have been exposed to whatever the problem is. The best way to prevent illness from coming home with you is to walk away. If you really find a fish you feel you must have, then take it home to a quarantine tank for the first 2 wks. Most disease issues will be obvious within that time frame, and the quarantine tank provides a safe environment to medicate just the sick fish, and it prevents the new fish from spreading disease to the main tank before you're even aware it's sick.
I will always suggest someone have a quarantine tank set up whenever possible. It's easy, not really any maintenance, and saves a lot of money, headaches, and heartaches in the end.