Members of the VSI are bound to rules of quality as set by the members in cooperation with the independent audit company Conformiso. This agency performs an audit every year and submits a certificate if the member (still) meets the requirements. If talking to a member you can always ask for a copy of the certificate. Conformiso also audits companies who want to become a new member. On the Dutch part of this webiste you can download the document with the requirements of quality.