Deborah

It means "Je connais toutes les ficelles" but it is mainly used for work or Art. You can add "Je connais toutes les ficelles du métier" when you talk about your job !

Have you ever seen "L'été meurtrier", with Isabelle Adjani when she was young ?!

Exactly! When you add "-ard", this is very familiar and negative. Like a "bledard", who comes from a "bled", un village. By the bye, a mistake: "...les véhicules haut de gamme..." (contrary : "bas de gamme")