How we cite our quotes: (Part.Letter.Paragraph)
Quote #1
And he would never think of exploiting the gaiety he inspires. He is perhaps something of a flatterer, but his delicacy would disarm modesty itself. (1.11.1)
Unfortunately, Madame de Tourvel is deceived by Valmont right from the start. Why do you think she's so easy to trick?
Quote #2
As for you, are you not ashamed? You put yourself to the trouble of deceiving him, and he is, notwithstanding, happier than you are. (1.15.1)
For Valmont, a successful deception is nothing to brag about. To be worthy of respect, a lie must have a successful purpose. In this case, the Marquise is lying to her current lover about her ultimate designs, but, in Valmont's estimation, her lover is receiving more benefit from the deception than she is.
Quote #3
Madame de Tourvel has charged one of her servants with obtaining news of my activities, if necessary by following me on my excursions of a morning, as far as it is possible for him to do so without being observed. (1.15.4)
Deception isn't just something the "villains" of this novel do: even the principled Madame de Tourvel will make use of minor deceptions. She wants to spy on Valmont without him knowing it. Ironically, she's doing it to uncover his deceptions.