Sefer Chofetz Chaim Chapter 4, halacha 11,footnote 2 part 3

The reason why it is so important to be open, and honest about why you are inquiring about someone else, whether it is a shidduch, partnership in business, hiring an employee, etc. is because if you don’t it is very to lead the person you are asking into speaking lashon hara, placing a stumbling block in front of the blind. If he doesn’t know your purpose in questioning him, he might say things which don’t need to be said, you might prove him too much and he’ll divulge unnecessary information, or if you are trying to use subterfuge you might start asking about other people so that he won’t figure out who you really want information about which leads to a tremendous amount of lashon hara about a lot of people. Therefore the right thing to do so that you won’t be tempted to ask too many details about the person you are inquiring about and so that the one answering the questions will understand fully why he is answering and will know what is appropriate to say and not to say, is to tell him exactly what the reason you are asking him about someone. You can tell him to keep the inquiry a secret but you can’t tell him answer my questions truthfully you won’t be doing anything wrong because I need some info for my own benefit and I won’t share this info with anyone else, for as long as you don’t tell him exactly why you need the info it will inevitably lead to unneeded lashon hara.

In a similar vein, if someone inquiries about his son or relative who lives in another city, he has to inform the person he’s talking to that he’s just asking for his family member’s best interest, for example how’s his learning coming along, is he still in Kollel, how’s his ruchniyus, etc. those questions can only be asked with the caveat that if there is a problem you would like to and have the means and enough concern to try to fix it. Therefore you have to tell the person you’re asking that you just want to help your son or relative. Something applies to Kiruv professionals inquiring about those they want to be mikarev, bring closer to Judaism.

Lastly if one moves someplace else and one day sees someone from his old town he is not allowed to ask him how this guy is doing and that guy and ask about details of people lives. Though it is tempting and part of human psychology to want to feel connected to those you haven’t seen in a while, giving away too many details about others is still lashon hara, therefore you shouldn’t probe and expect detailed answers about you long lost friends and neighbors since there is no usefulness into the inquiry.