Look already work with classibase for a long time, the secret is to add key words related blacklisted.
Go on the panel:
Settings> Spam Filters
Abuse least: in my use with 3 and works great. The user adds to the announcement, but it sure will be taken down in a short time. the good thing is that I am working as showing you, is that the extent to which the spam ads are added, you will update its blacklist of words.
Bad word block: in this field add the words one below the other: