Comment by eviks

21 hours ago

The same way you sell your disks: find a buyer, send them the game files, they send you the money

> find a buyer

this buyer would rather buy off GOG than you, unless you give a significant discount (and even then, the trust is hard to establish).

Therefore, even if you might have a legal right to re-sell (which you really don't unfortunately), the actual sale won't happen.