"Ten francs ! Robbery"- Which robbery is suggested here? What was the consequence?

This line is extracted from Katherine mansfield' short story, The Fly which is taken from The Dove's Nest.

          The 'robbery' refers to here is the high price charged by one hotel keeper of Belgium from the  daughters of Woodifield. They are charged ten francs for a spoonful of jam. That was called 'robbery', for the price was excessive and unreasonable.

 After this incident, one of the daughters of Woodifield, Gertrude  brought the pot away with her to teach the hotel keeper a lesson.