A great practice to use, wish all stores would do the same, however to not still quarantine afterwards is pure blasphemy.
Ich is just a number of things people use quarantine against, and the quickest was to do so is the tank transfer method, and that takes 14 days. Any fish who entwrs system of copper for less than 7 days can still carry ich, before it drops off to reproduce. Copper is only effective in the free swimming part, and and tomites embedded into the fish is protected against copper until it drops off.
Corals are even tougher to quarantine, for if they are in a system with fish, can carry cysts, which means at least 72 days without living in a system with fish to break the cycle. That's just a fish standpoint, with no regard to aefw or a handful of other coral killers.
In reality, one should have a fish quarantine, no less than 30 days , unless using ttm, a coral quarantine, no less than 72 days, and an invert/misc quarantine, for snails, hermits, algae , etc (anything wet)
As you will see, without this, at some point you will lose livestock, and that is why you are able to find so many items used for sale.
Ama is great for minimizing damage and quarantine, but that should be the start of it, not the end
