and the buyer after having redeemed code went to paypal and report that the code doesn't work in order to cheat out of this deal. the kind of code in question here is downloadable content code for video game consoles.
even if you mention in your sales policy that this is final sale, no refund, as is etc, how do you word it so that buyer must accept the code as is so they can't come back and game you after they already used up the code?
will paypal even check your game console account as proof of not having used up the code? that's kind of impossible because any gamer can create multiple accounts for free.