Good info Norman - I have never thought about testing the water in the bag the fish come in, but makes good since.
It is one of the most overlooked steps there is. Fish can take a drop in salinity, but very few can take a rise of over .001 in a short period. You should ALWAYS check the bag water for salinity, and also if you buy a fish straight out of the bag when received at your LFS or ordered on line and has been in a bag for hrs, you need to for sure check PH. Both are critical parims to most fish. You can lower your PH in the QT tank with a small amount of vineger. There are a bunch of other reasons to always QT, but this is a big one if you are running a reef tank with high salinity, because like Norman said most stores don't keep their tanks anywhere near a reef tank for salinity. Sorry to hear about the guy, but as touchy as these guys are I would for sure have a QT up and running.