4. Providers of online intermediation services shall bear a reasonable proportion of the total costs of mediation in each individual case. A reasonable proportion of those total costs shall be determined, on the basis of a suggestion by the mediator, by taking into account all relevant elements of the case at hand, in particular the relative merits of the claims of the parties to the dispute, the conduct of the parties, as well as the size and financial strength of the parties relative to one another.