In the formerly monogamous advertising world, polygamy now reigns. The modern version of the client-agency relationship leaves many agencies longing for the "Mad Men" era of sole partnerships, 9-to-5 schedules and heavy drinking by 3 p.m. -- but those days are long over. Today, firms seeking integrated solutions will often hire several agencies at once, each acting as more of a vendor that delivers a specialized service rather than as a partner that fulfills all the company's marketing needs. Companies do still seek partnerships with agencies, however. Unilever's been working with Lowe & Partners since 1899. And GM has a long-standing relationship with Campbell-Ewald that dates back to 1919. Other household companies -- Procter & Gamble, General Electric, Kraft Foods and General Mills -- also boast established, lasting agency affairs. Does that mean these companies won't step out on their partners from time to time? Not on your life. And when that happens, agencies find their egos bruised by this transgression. To renew the partnership dynamic, they must start behaving more like holistic consultants and remember that customers choose vendors but consultants accept clients. To position your agency as an actual partner, stop thinking like a vendor. Focus on these six strategic measures to change how a client views you and your team's capabilities: 1. Know the client's business. Partners know more than one side of a client's business. Instead of focusing only on the marketing end, approach the business as if you're running it. Get to know the distribution challenges. Look for ways to improve the sales system. Even simply walking the production floor asking questions demonstrates your interest. Getting your hands dirty alongside the client and sharing your thoughts on the business as [...]