Did you already sent those 6 codes?
Did he already confirmed if 2 of your 6 cards are works?
where is the proofs if you getting scammed? From your screenshot i just see if he will pay once he confirm atleast 2 of your cards are works
It's impossible to determine whether a card is legitimate or not without actually activating it. There is no proof that OP can offer which would help his position, and there is also no proof that carlosiness can offer to help his.
However, the question to be asked is: how is OP able to sell the gift cards at a 75% discount? And if they are able to do such a thing, is it legal?
-- along with that, why are they not selling them physically? (granted, it is easier to do sales [bulk or otherwise] online)
this has already been the reason for whywefight's trust on OP's page.