An agent is supposed to disclose his or her agency relationship upon having a substantive discussion about a specific property with an actual or prospective buyer. What constitutes substantive discussion about a particular property?
There is a difference between a general conversation about real estate and a discussion about a specific property. If someone talks about general preferences in his or her own taste for homes, then that discussion is not about a particular property.
For example, a statement like I love (or hate) Tudor-style homes is about taste; meanwhile, How does this Tudor home compare to the one down the street, moves the conversation into a discussion about a specific property.