Edited excerpt from The Big Reference Check Scam! by Tim Sackett:
Stop accepting references candidates give you. Instead, during the interview ask for names of their direct supervisors at every position they’ve had. Then call into those companies and talk to those people. Even with HR telling everyone “we don’t give out references,” I’ve found you can engage in some meaningful conversations off the record.
(1) Cf. How do to reference checks: Mark Suster.
(2) This is the final post (for now) on how do to reference checks for job candidates. You can see the entire series in the section Reference Checks in Best practices for startups — a list by topic.