Dear Yaakov Doe,
You want to hear positive things about the person your going out with. It is worse to not know the positive, than to not know the negative. You say that knowing the individual, is a minus?!?
Any decent reference, wants the caller to realize what it is like to be with the person. You do not want your friend to be stuck with people who have a different image of what he/she is trying to project. Nobody ever said you have to believe the references a hundred percent. And I will not tell you if she/he has serious issues, as long as she/he is able to be married. Unless you specifically ask.
Come to think of it, this thread explains a lot of the phone calls I get.