As you're referring to the $88 cards I'll chip in my experience, which is that the perfect gift cards don't have a photocopied barcode on the back for activation, there's a cut slot showing the barcode from the actual card you'll use.
With those particular cards, I see little risk with an opened packet as long as the pin number has not been scratched off. Someone could create a duplicate card by taking the card number and expiry, but would need the pin number to extract any funds (and to check online to see if the card is active).
Sorry reading my post I can see how I have caused confusion (in heindsight I should have left out the reference to $88 GC), my concern was referring to the $100 coles MCGC's.
All I was referring to when I mentioned the $88 cards is the fact that I have a cough load of empty cards now, my concern being that some scammer who instead happened to have a lot of empty $100 Coles MCGC's could effectively substitute these useless Empty $100 MCGC's for unsold MCGC's, seal the packaging back up and wait for the unsuspecting purchaser to scan and pay for what they think is a cardboard packet containing an unused MCGC, but actually now contains a used MCGC.
Assuming I am not missing something, this effectively means being diligent enough to ensure a card is in the cardboard carton may not be sufficient, unless you can and do ensure you confirm the card in the packet relates to the barcode on the outside of the cardboard envelope.
I'm assuming and hoping there is a process that would prevent this being possible.