“Yes he worked with me on these dates. He performed some of the duties of a Junior Project Manager, and then he left. If he wanted to come back, I would request that he re-apply and go through the recruitment process.”
“Yes he worked with me on these dates. I would ABSOLUTELY work with him again. No question.”
By law, you cannot share any real negative feedback about someone who worked with you, or you will open yourself to slander.
However, when I am interviewing a promising candidate with whom I want to make an offer, I would reach out into my network and do some gentle probing.
“Would you hire him again?”
“If I bumped into her manager at a pub, and asked what she thought of her, what might she say?”
If you are sub-par
If you are not a team player
If you are a fan of “short cuts” and “short term thinking”
If you are lazy
If you do not care about the quailty of your work
If you lack integrity
… people will find out.
Sure, there are the odd managers who might not like you because of personality clash, but if you are good at what you do, most people will know.
Integrity is what you do even when no one’s watching.