L'oiseau wrote - EDIT.
"I don’t think a proffered kiss would go down too well with a tetchy fonctionnaire, though! ;-)"
Very true - you have to assess the social situation and pick your victims!
The most difficult interview I had with a fonctionnaire was after we had sold our tractor, sans carte gris (long story). The buyer later decided he needed a carte gris or wanted his money back.
We didn't have the complete legal paperwork so I went to the prefecture in great trepidation - bonjour, ca va? etc.
The lady checked everything and looked very doubtful, but she saw that I was almost shaking with anxiety. Eventually she said d'accord, je l'accepte. Or something like that. We got the carte gris.