I use jobberbase, http://www.jobberbase.com/ , on a site http://jobsinireland.org/ it doesn't handle payments, but the verification of jobs is easy, as it sends the admin a link to approve the submitters first job. After that they can post again with out the check.
sure it's possible, but why would you want to integrate it in something else ? It's a stand alone software that can do most things that a jobsboard should do.