How we cite our quotes: (Part.Letter.Paragraph)
Quote #7
Provided with my first weapons, I practiced using them: not content to be inscrutable, it amused me to assume different disguises, and once sure of my demeanour I attended to my speech. I regulated both according to circumstances, or simply as the whim took me. (2.8.26)
The Marquise is the queen of the lie. She's practiced it from a young age and it's now second nature. It's her talent for deception that allows her to fool everyone into thinking she's a pure and respectable person.
Quote #8
In vain had I been told and had I read that it was impossible to feign the feeling [love]; I had already observed that to do so one had only to combine an actor's talents with a writer's wit. (2.81.29)
This was probably the life lesson that most enabled the Marquise to be such a success; she can totally and convincingly fake love. Valmont prides himself on that same talent but it eventually fails him.
Quote #9
In order therefore to attract one party and repel the other, I was obliged to advertise an indiscretion or two, taking as much pains to mar my reputation as I had meant to take to preserve it. (2.81.31)
Don't assume that because Madame de Merteuil is willing to admit some of her faults in addition to some of her virtues, she's an honest person. She's interested in creating an image of herself, or in this case two images meant for two different audiences.