Ever had someone that scammed you( usually a better scammer than you, but hell, sometimes they are

).
I have managed to do this thing several times.
When someone scams you, be sure not to logout of the blizz account page. If the scam you, just quick activate the parental control feature for your email. That can only be changed by calling blizz.
You will need to verify the parental control from your email, but if you are loged with one page on the account management page, it is done automatically, you dont need to put account & pwd again.
So, if some1 scams you, activate the parental control, make red all the hours there, and he wont be able to log into wow.
Hope it works for you.
Edit: Also, if you scam some1 for gold, delete theyre chars, create them on a trial account, and then go to parental control and enable it on one of your emails, so the guy wont be able to login, his toons will be deleted, and probabily the gold will never be recovered.