I hate these new social media trends where people walk up to strangers on the street and ask things like "how much do you pay in rent" or "how much money do you make a year"...ignore them!
These can be constructive informations if you are looking for a place to rent or to compare the yearly income of a professional who shares the same career you belong. I have to know how much people are paying for a rent in a determined area if I'm moving myself to live there, otherwise I might be going to rent a place which charges an abusive price from me. Moreover, I have to know how much professionals from my working field are being paid to conclude if the payrates being offered to me are inside that payrate margin. And if I can help someone else with these informations about myself, I'm glad I can help enlighting them on these matters, since I have also been on their shoes in past situations, so I know how it feels to be confused about it, while having no one to ask about.
If there is a constructive purpose behing the doubts and questions, there is nothing wrong with that. I think what should be avoided are curious, gossipy and whisperous people who just want to know details about your life for no reason at all, and especially to kill some time and have something to talk to other people about, since they don't live their own lives as they were supposed to do. Then of course you shouldn't give any personal details to them, because there isn't any productive purpose from their side.