Mister-Gency: One thing Valve used to do is have the code printed on the receipt. The cards can just be there for show and to let people know they can buy them, then keep them when making a sale. That should cut down on the cost of producing the cards.
Sure - if that's true, all you practically needed would be one copy of a "GOG Gift Card" per store, maybe one per amount ($5, $10, $50,...).
I never bought one, so I don't know from own experiences how it works exactly - however, I found online comments, about how you have to scratch off a panel over the code to see it - which sounds like you get a physical card - not just a receipt.
And you write "One thing Valve
used to do is have the code printed on the receipt"...which would imply, they don't do it like that anymore?
But apart of the above:
it's not done with just sending a card (
or several cards) to any store in the world.
First you have to find distribution partners - those differ global wide, not every country has a Walmart, or a CostCo.
Then you have to find out, what their cut will be - they don't keep those cards in their store for nothing - you know!?
Handle out a deal.
Then you have to find a manufacturer for those cards.
Find out what he charges you for the production.
Pay that manufacturer.
Then that manufacturer has to have a production window open, in which he can produce your cards.
Then you have to ship those cards to your distribution partners.
Pay the shipping company.
And after all that, you sit there and wait, if all the money you invested thus far, will come back in form of revenues...or if it was for nothing.
Oh, and let's not forget - you'll have to pay taxes in every country, where you sell your cards.
That eats a part of your expected revenues up, even before you see them.