Une bête à bon Dieu (or, bête à Dieu) = A ladybird.
Plus fin que lui n’est pas bête = It would take a smart man to deceive him.
Beurre
On ne peut manier le beurre qu’on ne se graisse les doigts = One cannot touch pitch without soiling one’s fingers; If you have to do with money, some will stick.
[“But I think they that touch pitch will be defiled.” Much Ado about Nothing, iii. 3.]
Il faut faire son beurre = One must make a profit; One must feather one’s nest.
Ça entre comme dans du beurre = (fig.) It is as easy as anything.
Bien
*Le mieux est l’ennemi du bien = Leave well alone.