Buying fish and Live Rock question

[hummer]

Hi,
I started my salt water tank about a year ago (I use to do freshwater). I'm still fairly new and learning. I have 2 questions:
1. I alway buy my fish from stores specializing in Salt Water. Are there any issues from buying fish from normal pet stores like Petcetra or PetLand?
2. Is there a way I can tell the health of my Live Rock?

Thanks for any help you can provide.