I think that's going to vary from agency to agency... so clear the rules with the listing agent, as to what they expect.
If you were sitting one of my properties, I'd say: While you're there to connect with potential buyers and sellers, remember that you still have to "represent" the property, our agency and the seller.
So never badmouth the property (ie: This house isn't right for you... I have something better down the street).
You're trying to build a relationship with a potential buyer, but don't say something like: "They're overpriced, I can help you get it for less."
You never know who you're talking to... treat everyone as though they're the seller's relatives. Who knows, they could be.