Wow what a deal! The fish at Petco, at least in my experience, have been very poorly cared for, so if it was me I wouldn't buy any livestock from there...unless your friend knows more about the husbandry of the fish/inverts. If nothing else and you still want to buy from them, don't hesitate to ask if they can put some food in there to see if the fish eat (good indication that they are happy and not stressed
). Also it might be good to ask other questions and check for ich/other parasites. You wouldn't want a fish getting sick and dying and spreading the illness to your other fish!