Car Part Homologation

Looking to understand how aftermarket car parts/wheels get homologated. I understand that a 3rd party like DTC or FAKT need to test and verify the tolerances and strength but who determines why only certain dealers or resellers are allowed to sell the Swiss homologation certificates needed for the MFK if the part has been tested?

I am trying to get an aftermarket wheels and looks like only the one "official" seller in Switzerland has these certificates. Im wondering why/how they get the monoploy on these certificates or if ones are allowed to sell this.

Any help on this would be appreciated.