Most live rock is really "mostly dead" rock.
By the time you get it, most of the good stuff has died off and more will die off after it gets in your tank.
Places like tampabaysaltwater (where all my rock came from) gets it out of the ocean sometimes less than 24hrs before they ship it to you, by freight, and you pick it up at the airport the same day. Now THAT is live rock. :D
Just because they show you some pictures on the internet of rock with purple stuff on it doesn't mean it's really all that live. Buy from a reputable place like biff mentioned.