Hmm, yup Frontier did not see a penny of that sale, G2A got 10% the seller got the rest. As for bogus keys, as I said, it's not like sellers on G2A haven't been caught doing it before... Ubisoft has caught them, and deactivated keys, EA has caught them and deactivated keys. Those two stores have both allowed keys to be activated as legitimate & then subsequently revoked them. A quick search on steam also reveals similar stories about G2A & other key resellers markets... So yes, definitely not true...
Not to mention all the times where the sellers then request the key revocation themselves even if they are legit.
Oh, and actually yes, a multimillion dollar company like valve will allow a bogus key to be iadded to your steam account if it looks legit, right up to the point where it isn't, be this Years, months, days or even mere minutes down the line...