ChofetzChaimDaily 17 Elul 9:1 If you know bad things about the ploni that R wants to enter partnership with, you must tell R, provided that you fulfill these conditions A. its definitely destructive to partner B. must not exaggerate C. must intend ltoeles (be sure that R will actually take your advice) D. seek alternative methods first E. it cant
ChofetzChaimDaily 16 Elul 8:4 Rechilus is asur even if the comment ploni made wasnt so bad, ex. When Sarah said and my husband is old Hashem didnt repeat that part to Avraham. 8:5 if someone tells you a secret, you may not repeat it, it can damage him and isnt derech tznius.