Mori_Yuki: [...]The only thing customers would have to know, if GOG introduces gift/voucher cards as an option, is: If they are purchasing more than one gift-card at a time, with a value of 50 Euros (or equivalent in foreign currencies) per card each, not to attempt to use them all in one go, but only one card to add 50 Euros. I am not sure, how much time must pass, before the next card/voucher can be redeemed, this would be something you'd have to look up yourself. Otherwise, if a customer tries to redeem 2 cards, at a value of 100 Euros total, they'd have to have means to provide proof of identity, which is on the shop or processor to provide to be able to use the cards/codes anywhere on the Internet. [...]
Just as one data point: With Paysafecard, there apparently is a five-minute delay
on the vendor level between purchases exceeding 50€, at least in my country. Meaning: If someone in front of you buys 100€ via Paysafe, and you want to do the same immediately after, you will have to wait for the vendor system to unlock that option again. I know this because it's happened to me recently.
On the flip side: Once you do have that 100€ Paysafecard, you can split it into two purchases of 2x50€ on GOG without proof of identity, and without any delay. If you want to make it a single 100€ purchase, you will have to register an account with Paysafecard, including proof of identity.