Why scammer is not banned?
Scams are not moderated. So scammers do not get banned. Rather are tagged by users so others can know that they are likely to scam. This is how bitcointalk has been working since the beginning.
That's not true, though. There used to be a "scammer tag" that was applied by staff. They did away with that a few years ago for this great system. Ahem.
OP, this'll teach you to read feedback and do due diligence before doing deals. Don't know why you couldn't just use yobit or some other exchange. It's not like you have to give them personal info when doing doge--> btc trades.