How can I verify the master plumber license number of a plumber. I called the city licensing bureau and they have no master plumber license for this plumber; however, they said a plumber may be licensed in one town and operate elsewhere. The plumber has not produced a license and for legal reasons I cannot ask him for it again.Does anyone know if plumber must be licensed in city or state of operations? Is there a central repository of master plumber license numbers? Thanks.