mike_cesara: You'll be fine mate. Just don't trust random people, especially on the internet.. And chargeback, you get your money back and loser will get nothing, one more red flag on his steam account.
pferreira1983: If the keys are used, can I get my money back? How do they believe I'm telling the truth for them to provide a refund?
Keys will be revoked and games removed from scammers library.
That is a common practice at g2a/kinguin which is completely black market. But you should check your account there anyway, if you didn't pay attention or simply out of luck, you already got
some paid subscription and will pay them several quids every month for some kind of
protection or something. They will not give any money back, so chargeback is the only option I believe.
You may also chargeback or simply contact humble support and explain situation. Do it before time runs out and get your money back. And good luck finding a job mate, panically need one as well ; )