I believe what they are looking for is drug usage, alcohol abuse or crimes of moral turpitude (google it) along with not being suceptible to 'monetary persuasion'. Someone in very deep debt just struggling to get by could see that $10K in cash as a salvation and look for more next month.
Had clearances with specials for years while a contractor (DoD and a few other 3 letter agencies) - subject to polygraphs every six months, financial reviews whenever they wanted (usually didn't actually know about them), etc... oh, and had to fill out pages of paperwork just to go on vacation... a credit check is nothing - had to do one for my real estate license (we hold people's money and advise them on large transactions).