I always assumed that there could be halachic problems with sharing financial information that could end up hurting someone. I know when I was looking into the possibility of renting a particular apartment and I asked the previous renter how much she had paid, she didn’t want to tell me, because she thought it could be problematic halachically since I might then go to the landlord and say, “I know your previous tenant only paid $x so can you give me the same deal?” I also always tried to be careful not to tell people how much rent I was paying for the same reason (in case I left and someone else wanted to rent who had heard what I was paying and wanted to be able to pay the same amount).
I have no idea if there is such a halacha – I just always assumed that according to halacha, you should not give over information that might hurt someone else.