someone offered to me blizzard games for my steam game.

Keys can always be acquired with a stolen or hijacked creditcard.
I wouldnt trade with him
Those games can get revoked weeks after you activated it

Check if he has some trading rep anywhere and decide then if you want to take the risk

even if he is not a scammer I don't think its worth it

yeah I think it still can be refunded from ur account if it's bought with stolen card,check his rep if he has 100+ go for it or 90+, since blizzard have differnett handling control than steam :)

he hasnt steamtrades rep and there are 2 reps on his steam profile. He bought these games from g2a.com.

I googled it with his nickname and i found someone, same profile but real profile so he is a cheater.
Thanks everyone.