It can be very difficult to get any of the information you really want when you question an applicant's job reference. Modern employment laws make it hard, if not impossible, to ask any specific questions about a former employee. If you are going to ask one question, however, Jack DeBoer has the perfect one.
DeBoer wrote in his book "Risk Only Money" that many employers these days don't really want to shoot straight with you when it comes to discussing employees who were not that great. They don't want to face the possibility of a lawsuit if their answers costs that person the job, even if it's hard to prove it. If you are going to get the information you need, DeBoer wrote that you should ask the following question: "If you needed the skills of this employee, would you rehire this person?" This is a great question to ask because it's a simple yes or no answer that requires no further explanation, and it allows the employer to tell the truth without violating any laws.
DeBoer also suggested that hiring managers should learn to read between the lines when listening to an answer. For example, if you ask how trustworthy the former employee is, listen for any hesitation in the answer. Anything less than "Oh, absolutely!" can be a signal that you aren't getting the whole truth. You can also try asking about the employee's performance rather than their character, as DeBoer wrote that there are fewer laws restricting those kinds of questions.
Employee screening can sure be difficult, but the tips above should make it a little easier to get the information you really need.