Just looking at your sig, swordtail koi? I'm confused, surely not the potentially huge carp that should be kept in nothing less than a pond?
From what I've gathered on here (I'm not from the US myself, we don't have petco), this seems to be a shop to avoid, I may be wrong but I don't see why the delivery would be any better than buying them in store. If you have a local store which is trustworthy and where you've already got your fish from, go there.
Out of interest, what fish?