Their morals and ours

You can be a good, loving French couple, model parents who are hard-working and obsessively frugal, and yet run a black-market operation out of your high-security villa in Béziers, selling shoes from your old store and "satisfied or your money back" products scammed from all the region's supermarkets.
To each their own morals!
You can be affectionate neighbors, doting on the old lady next door who has promised you her small inheritance, and yet poison her for two euros and fifty cents by simply slipping her a "deluxe paella" that's gone off.
To each their own morals!
But then an heir of that neighbor shows up out of the blue and moves into her house !! That's when the gloves come off, because you know what they say: there are honest folk and then there are the other kind... But where's the morality in all this? Not necessarily where you think...