One of the biggest concerns for immigration is that the applicant is primarily interested in immigration status to Canada. Marriages of Convenience can occur when there is agreement between the parties (e.g., when the applicant pays the sponsor for the sponsorship) or when the applicant has ulterior motives.
Two recent changes to IRPR were aimed specifically at eliminating MOCs: the two year conditional PR for sponsored partners and the five year bar prohibiting anyone sponsored as a partner from in turn sponsoring a new partner.