No store is safe. They most likely had fish that were sick before just not showing symptoms. If they are not medicating the tanks then it is spreading like wildfire and they are losing huge amounts or fish and money,p painful either way for a small business. If they are treating the tanks it doesn't not mean the fish doesn't have anything. Just that the fish will show symptoms once the medication load lessens, because most medications are not in therapeutic levels due to top off and water loss in those systems throughout the day. They are doing the best they can, but those fish are not in those tanks long enough for the medication even if it is in high enough levels to actually treat the sick fish.
In short, support your LFS but ALWAYS quarantine everything. I will buy any fish that shows no symptoms of illness even if the fish next to them is ill. I always dip (hydroplex) and quarantine everything or you can expect loss at a high price. Support the little guy if they are trying to do things right, just stay informed.