Short answer
Trusted references can provide useful information about character and conduct, provided the inquiry is fair and respectful.
Islamic Guidance
What Islam teaches
Islam encourages verification and warns against acting on unreliable information.
Practical Guidance
What you can consider
Speak to trustworthy people who genuinely know the person and ask relevant questions rather than seeking unnecessary private information.
Sources
Qur'an 49:6; Qur'an 49:12.