Whether you are the person asking for information or the person being asked for information, your intentions should be totally leshaim Shomayim (for the sake of Heaven), to help bring about a marriage that should be and to prevent any marriage that the Torah says should not be.

A person asking questions about a shidduch (the boy or girl, a relative or advisor, a rabbi or rebitzen) is allowed to ask as many questions of as many people as needed. It is meritorious to investigate carefully and to do all of the "homework" that you see fit. The more people you speak to, the more you are likely to uncover inconsistencies, fabrications and meaningful data. The Chafetz Chayim says that questions must be specific and you must reveal why you are asking (that it is for a shidduch), and the other person is not obligated to give information to you unless you make clear that there is "to'elles (beneficial, constructive purpose)" that constitutes a halachically permissible reason to speak about a person. Another way of looking at this is that questions and answers must be relevant and purposeful so that your talk will not bear any guilt of lashon hora. Pirkei Avos (chapter five) says that one who is an intelligent person will not interrupt, will only ask to-the-point questions, will only give answers after deliberation and according to halacha, will answer the first thing first and the last thing last, will say that "I do not know" about what he does not know, and he acknowledges the truth.

It is entirely alright to appoint a shliach (representative), or more than one, to ask information because this may obtain more, better or more accurate information (e.g. his Rosh Yeshiva talks to her seminary's principal, his uncle goes to shul with her father's neighbor, her school friend knows his sister).

The person receiving/replying to questions about a shidduch must realize that (s)he is playing with lives. Rabbi Chayim of Brisk said that speaking against a person of marriageable age is killing, and only the Sanhedrin (Torah Supreme Court adjacent to the Holy Temple) of 23 judges has the authority to execute. We must be very careful. There are many considerations about what to say and not say. We cannot say lashon hora but, on the other hand, "Lo samod al dam rayecha (Leviticus 19:16; we cannot stand idly by while our brother bleeds to death)," we cannot cause michshol (another to stumble into trouble or a mistake) or nezek (harm, damage).

If you do not know something, do not speak as if you know. If you know something in general, but not specific details, you can ask for time (to call a rov, or find out from a halachically reliable first-hand source - not hearsay or rumor) or say "I don't know." You may not speak for personal motives (e.g. hate, revenge, subjective opinions about who you think the boy or girl ought to marry). If you are asked a question directly, you cannot evade it nor lie.

There is greater responsibility for a close friend or relative. If you are asked by or about a close friend or relative, you can offer additional information over what was asked about, such as information about what is not suitable in the shidduch or you can offer information about minor defects.