How we cite our quotes: All quotations are from Harry Potter and the Half-Blood Prince.
Quote #1
BELLATRIX: Cissy, you can't do this! He can't be trusted.
NARCISSA: The Dark Lord trusts him.
BELLATRIX: The Dark Lord is mistaken.
Here, Bellatrix and her sister are talking about Snape. Dumbledore thinks Snape is working for him, and the Dark Lord does, too. Only Snape knows who's getting zoomed.
Quote #2
SNAPE: As it so happens, I'm aware of your situation, Narcissa.
BELLATRIX: You? The Dark Lord told you?
SNAPE: Your sister doubts me. Understandable. Over the years, I've played my part well. So well, I've deceived one of the greatest wizards of all time. [Bellatrix makes scoffing noises.] Dumbledore is a great wizard. Only a fool would question it.
NARCISSA: I don't doubt you, Severus.
Bellatrix and Narcissa are at opposite of ends of the "Is Snape loyal?" debate. Bella doesn't trust him for a second, but Cissy seems to believe Snape.
Snape himself doesn't seem to mind that the sisters are airing the elephant in the room, and assures them he's been pretending with Dumbledore, not the Dark Lord.
Quote #3
HERMIONE: You really shouldn't have done it.
HARRY: I know. I suppose I could have just used a Confundus charm.
HERMIONE: That was different. That was tryouts. This was an actual game. [Harry takes the full vial of Felix Felicis out of his pocket and shows it to her.] You didn't put it in. [Harry shakes his head.] Ron only thought you did. [Harry nods.]
And now, for a completely different form of deception: Harry let Ron think that he'd slipped him a lucky potion to make him awesome at Quidditch. He hadn't really given the potion to Ron, but the trick made Ron confident enough to actually be awesome at Quidditch. We'd say this is pretty much the best kind of lie, no?