A couple of thoughts on your post
First, agent licensed by the Dept. Of Real Estate is REQUIRED to reveal that they are a DRE licensee.
Second, if they are a Realtor, they need to reveal that too. (Realtor Code of Ethics, http://www.realtor.org)
Third, as a seller they are required to follow all the rules of disclosure to anyone, just as the public is required.
During the "discovery period" It is likely that liens against the property will be discovered (if they were recorded against the deed). Judgements that are pending may not.
However, if a buyer finds out after the purchase that there are judgelments, (I am NOT an attorney, this is not legal advice) could probably sue the previous owner. It sounds like a mess to me.
If you have proof I would take the evidence and report him to the DRE and the local association of Realtors. You can look they up on the DRE website and find out who the listing broker is...