It used to be the best source [of information about potential hires] was to check job references. Nowadays, though, very few employers will give a honest job reference, or will provide any information at all. I know I am guilty of that — my company does not allow any manager to give out performance data on past employees. I only needed to be sued once over somehow interfering with someone’s living by giving honest information about that employee’s reliability to change my behavior.
I once called another library to ask about a potential hire. The director said, "We have a legal agreement not to say anything about Mr ___'s job here." No more needed to be said.
On the other hand, I have gotten glowing references from previous employers for employees who turned out to be awful. More than once. Thank God that you can fire an employee for any reason before he or she becomes a permanent civil servant.