According to the Bundesgerichtshof (Federal Supreme Court) clauses contained in the terms and conditions of airlines that specify a processing fee in case a booking is cancelled or a flight is not taken, put customers at an unfair disadvantage and are therefore invalid.
After a decision by the Court of Justice of the European Union (ECJ judgment of 06.07.2017, C 290/16), this view is not contrary to the price freedom granted to airlines.