Hilchos Lashon Hara, chapter 2, section 13

If someone revealed to his fellow in front of three people details about his business and trade, and suchlike, that one is generally forbidden to reveal to another person lest this causes harm or pain to the speaker – if he spoke before three people, this indicates that the speaker is not concerned about this. Therefore the listener will be permitted lechatchila to relate it to others, so long as the speaker does not indicate that he is particular about the matter.