Dear Mr. or Mrs. Müller,
there is no legal requirement to participate on a course and/ or to pass an exam. Yet most of the employers very much appreciate this. Increase your know how (and your market value) by participating in courses by renowned organizations like e.g. the TÜV, DGQ. See also the "networking" aspect.
: Muss der QMB eine nachgewiesene Qualifikation besitzen? Z.B. Bescheinigte Teilnahme an einem Seminar?