I work at a research institute attached to a university. My boss and I decide to hire one of our interns into a temp to full time roll. This requires two positive references. Candidate lists 3, me (I was her supervisor during her time as an intern), her undergrad advisor, and her old boss at a tutoring center.
Her undergrad advisor gives a good reference, really aligns with what I had seen from the candidate during her internship.
Her previous boss absolutely tears her apart. Says she was the bottom ten percent of workers, lazy, always on her phone, argumentative, bad to work with, the whole nine yards. Really shakes me to my core, like I totally misjudged the character.
Fortunately I have a great supervisor and colleague, and they basically tell me that they trust my assessment more than this other lady's, so I decide to fill out the second positive reference myself and take the risk.
BEST. MOVE. EVER. She's been working with us for about a year now full time, and she's saved multiple projects from the fire, has been willing to work on whatever project, has learned so much, and is super reliable.
So yeah. In conclusion, f you random old boss, and always go with your gut.