Any fees charged by an intermediary for the services mentioned in Articles L. 228-29-7-1 to L. 228-29-7-3 shall be non-discriminatory and proportionate to the costs incurred in providing these services. Any difference in charges resulting from the cross-border nature of the service shall be authorised only if it is explained and corresponds to the difference in costs incurred in providing the service. The charges shall be made public, under conditions laid down by decree in the Conseil d’Etat, separately for each service mentioned in this article.