Well. For one, staffers do not make the decisions for fanlistings they themselves have applied for. Usually, a staffer who decides they'd like to apply for a subject and if that subject ends up having more applicants then that staffer passes the decision onto another staffer or to the senior staff.
An example of this is when I applied for the series Johnny The Homicidal Maniac over at TFL. Obviously, I can't be fair and unbiased since I staff the comics category, JTHM being a comic series. So I made a request for another staffer to make the decision for me. Someone volunteered and from that point on treated it as he/she normally treats applications. [In the end, I didn't get approved - oh well! Heh.]
Another example, if you're looking for a TAFL related one, is that I am helping out with the C/I applications. However, I informed the C/I apps staffer which subjects I'd applied for so that I wouldn't get those subjects to make decisions on.
The only case I've ever known of, of staffers ever approving themselves, is for subjects that have no other applicants - except for the staffer. :bounce: If that's the case, then I don't see there being a problem, since no one else applied.
I hope that helps with your curiousity!