Hilchos Lashon Hara chapter 4, section 11
And understand clearly yet another essential rule in these matters. If someone wants to get another person involved in his affairs, for example, to hire him as an employee or to work with this person in arranging a martial match with him, even if he never heard anything negative about this person until now, it is permissible to make careful inquiries about him to learn more about his character and situation. Even though it is possible that during these inquiries people may speak badly against the subject of the inquiry, nevertheless it is permitted to make them. These inquiries are permitted because their sole purpose is to protect and benefit the one who is making any inquiry in order that no damages or contention will occur in the future that will result in a desecration of Hashem's Holy Name, G-d forbid. But it would be necessary to tell the respondent the reason of the inquiries, so that he won't tackle him in Lashon Hara. Then even if the friend will speak badly against this person, it will be for benefit and not Lashon Hara. The respondent must be extremely cautious not to exaggerate his evaluation of this subject. But if the questioner does not explain the reason for making the inquiry, then it appears to be obvious the questioner is committing the sin of leading someone blindly into stumbling into a sin. The questioner is causing the respondent to commit an esur if he speaks slanderously about the subject of the inquiry even if the characterization is true.
