Mediator Certification

Hamline Law Professor Sharon Press has done a lot of good writing on mediation and here addresses mediator certification.  She sensibly argues "that a certification process is incomplete unless accompanied by an adopted standard of conduct, a process for handling complaints, and the authority to remove certification from an individual if warranted." 

I am particularly interested in the government/private questions regarding mediator certification.  Should government (including courts) ever require parties to use a mediator who has been certified, as opposed to just requiring them to mediate?  Should government subsidies for mediation be directed only to mediation conducted by certified mediators?  If these sorts of questions are answered "yes", then determining who gets to the do the certifying becomes an important legal and even political question.