Questions that an employer should ask when checking personal references include whether the candidate can be rehired, if the candidate was actually an employee of the company, how much the individual was paid, whether he was punctual and if the candidate got along well with his co-workers and supervisors. When checking personal references, employers should also ask how far the individual advanced in the company.
Additional questions to ask include if the candidate can be trusted, which is especially important if he applied for a position that deals with money or payroll. Hiring managers can also ask how the individual handled pressure and stress. Checking the person's online activities and social media profiles can also create a better idea of the type of employee he's likely to be.
It's best to speak with a manager who worked directly with the candidate in order to get the best impression about how the individual worked and his dates of employment. All references provided should be professional rather than personal. Talking with friends and family of the candidate is unlikely to yield useful information.
Open-ended questions are better than questions that can be answered with a simple "yes" or "no." Hesitation, pauses and other sources of subtext can be useful to learn more about the candidate in question.