Additionally, even if you get a reference who only speaks good of the person, you can often tell something by the qualities they list and the ones they omit. If you call 3 references and every single one tells you that the guy is good-looking, friendly and sweet and is always doing chesed, but no one mentions anything about his learning or intelligence, chances are that he is not a genius and is not a masmid or they would have mentioned that. If learning and/or intelligence are very important to you, that might signify that he is not for you.
Likewise, if everyone talks about how Frum he is and how machmir he is on halacha and what a big masmid he is and no one mentions anything else, that might be a sign that he is not the warmest, most sensitive person, and w/o jumping to conclusions, you might want to look into it further. This was actually a real example that happened to me. I looked into it further and found out that that was the case and the reason for his divorce. I chose not to go out with him.