Right now the only way to do it is to specify clearly in the campaign
description that you will not allow .cn domains. If you do get posts
from that domain you can dispute the post and you will not have to pay
for it.
One think you may want to try is a new feature we are testing with
some customers that allows you to approve a blogger prior to posting.
When a blogger applies to post, an email is sent out with the approval
request and you get to approve or reject. Currently this feature is
only in testing but if you are interested we can use it for your
campaign. Just shoot me an email.