They do have their "quiet" times. But actually the main reason are the ones at the LFS are either wildcaught or pen raised. Mine are captive bred and have been dealing with people all their lives. They are trained to know what a person coming near the tank could possibly mean. The WC or TR ones know humans pull them from the water, bag em up and transfer them all around.
Now, if an LFS gets in pure captive breds and puts them in a tank with LS/LR and even appropriate tankmates and environment, they could still freak and cling for awhile. They were raised in barebottom plastic tanks without rocks or "friends". All they know are plastic hitches and PVC... and that humans = food. They will hitch all over your hands.
But most fish... any fish, don't show their natural behaviour at an LFS anyways.