OP, anything above 0.005 BTC should be done by escrow. You'd be surprised at how little people scam for, i've seen people scam for even $2 on this forum. By using a free escrow service you're denying the scammers a chance.
Seems like there are at least a few others that got scammed by the same user which leaves me no doubt that this user is only here on forum to scam, and nothing else.
Will the admin ban this account? The guy is still steals the money of persons like me.
Nope. Admins do not ban scammers because there are simply so many of them, it makes banning every single one of them impossible. That's why you need to read the trust ratings of a user before you deal with him thoroughly.