Why the standard questions fail
Would you rehire this person invites a yes, because saying no about a former employee is a thing careful people avoid. What are their weaknesses invites a rehearsed answer, usually a strength wearing a disguise.
The problem is not that referees lie. It is that vague questions give them permission to be vague, and most will take it, because being specific about a former colleague feels like a risk.
Ask about circumstances, not qualities
Tell me about a time the plan changed suddenly. What did they do first. This asks for a story rather than a judgement, and stories are much harder to make bland.
What kind of problem would you bring to them before anyone else, and what kind would you take somewhere else. Referees answer this honestly because both halves feel fair. The second half is where the useful information is.
Who did they make better. A person who develops the people around them leaves evidence, and a referee can usually name someone within a few seconds or cannot name anyone at all.
The question that does the most work
If they started with you again on Monday, what would you set up differently for them. This is not a question about the candidate’s flaws. It is a question about the conditions they need, and it gets answered generously because it sounds like advice rather than criticism.
The answers are startlingly practical. They need a clear line to the person who decides. They need to be kept out of that particular meeting. They struggle when they inherit somebody else’s half finished work. All of that is directly usable in the first month.
Who to actually call
A former direct report is worth more than a former manager, and almost nobody asks for one. Managers see the output. Reports see the method, and the method is what you are buying.
One caution. Ask permission and go through the candidate. A reference call that reaches somebody’s current employer without their knowledge does real damage to a person who has done nothing wrong, and it will cost you the hire.