I don't buy all my fish from one place. I think it's better to shop around, but with care. One store can have good practices, but things change—staff, supply, even water quality—so it helps to have options and not be totally dependent. Plus, no single shop always has every healthy species I might want.
What matters most to me is quarantine and observation, no matter where the fish come from. I look for alert behavior, clear eyes, full fins, and a clean tank. If a store has dying or sick fish visible, or tanks look dirty, I walk away. Some stores are better for specific species or get oddball types more often, so it's smart to visit a few.
I avoid risks by keeping separate quarantine tanks. Even with a trusted shop, new fish spend time in quarantine so I can watch for hidden issues. That way, whether I bought from my usual shop, a different local store, or even a club auction, my main display tank stays safe.
Bottom line: flexibility is good, as long as you pay close attention to fish health and clean tank environments in every shop you visit, and always quarantine before adding anything to your display tank.