Frankly, I have never understood how a reference check becomes the final statement on the capabilities of a candidate.
Reference checks may be relevant to assess a person's general character, but they can never be sufficiently reliable viv a vis a candidate's qualifications for the position unless a candidate has successfully bluffed his/her way through an incompetent screening process / screening team.
In a man eating man scenario that we continuously encounter in the post meltdown scenario, many commentators while giving references often tend to lie about good candidates by giving negative references to retain openings for their own near and dear ones who may be incompetent but will succeed in eliciting favorable references due to their connections. Lying can be both ways.
The bottomline is that this process is useless which explains why many HR professionals merely take it as a formality and complete the exercise superficially.
Come to think of it, if reference checks were even half as useful as they are made out to be, the World would not have seen the economic bloodbath that we are still struggling to emerge from over 2 years after it first struck.