I read through a public list of the decisions on clearance appeals a couple of years ago, and financial concerns were a very common reason for denied clearances. (Might have been http://ogc.osd.mil/doha/industrial/)
Another thing I found interesting from that list was that a lot of concerns (e.g. earlier drug consumption) could be successfully addressed, but lying on the questionnaire was pretty close to an absolute no-go. I also expected a lot more denials for political opinion to stop ideologically motivated whistleblowers, but barely found any such entries.