Different crab in my order?

[hillegom]

It really doesn't matter whether you buy from a house business, or an LFS.
Ich could be on the gills only, where you won't see it and when the fish gets stressed, like when its transfered to another tank, then the fish's immunity is compromised and the ich spreads. Not only on the new fish, but possibly your fish. Your fish could have had ich and the stressed new one gets it.
Only way to, IMHO (others will disagree), eradicate ich is to QT, or TT method all fish.