When the federal government did a background check on me, they asked me for a list of references to contact. My uncertain recollection is that they ignored it and interviewed my neighbors and other contacts instead, as if what I had given them was a list of people not to bother contacting because they'd only say good things about me.

I've been contacted twice for friends' security clearances, which is similar but probably more likely that the due diligence is actually done (and it actually matters).