one hand washes the other (and both wash the face)
All parties involved will benefit from helping each other and/or working together toward the same goal. Look, if you feature our company's logo during your campaign, we get a major boost in advertising visibility, and you get a bump in your campaign funding—one hand washes the other! The criminal organization has several politicians and most of the police force in its pocket, with everyone seeing a profit from illegal activities. One hand washes the other, and both are washing the face!