At the end of the day, a brand should own and manage its relationships with customers. It's not the kind of job a third party, even an agency, should handle for the long-term at least. The ultimate benefit of social media is observed when its built into the way a company does business, and having a third party between the brand and its customers makes putting that into practice difficult, if not impossible.
The best example of this is with community management. Many brands outsource all of this, not just for the short-term but indefinitely, which ultimately means the brand is missing the point of social media. It allows a brand to get closer to its consumers, and the less involved a brand is, the further away consumers are.
Agencies Can Help
Don't get me wrong. Agencies can and do help in managing relationships, especially at the beginning of a social media program when time and personnel are in short supply. An agency can play that role in facilitating customer relationships, putting processes in place, training internal staff and making sure all the pieces are in place before the end handoff to the brand. Having an agency manage customer relationships at the beginning allows for action to be taken while the kinks are worked out and processes are implemented.
Agencies can help, but over the long-term it's an unsustainable model. No matter how great the agency is, it can never know the ins and outs of a business and be able to manage customer relationships quite like the people behind the brand. So use agencies to fill in gaps, but don't let them become a crutch.
Plan for the Transition
A transition plan and timeline should be in place for any social media program that includes a third party maintaining relationships with customers. Understand who can take over internally, what will be required of them, how they'll do their job and what tools they'll need. An agency should be able to provide all of that information or at least a recommendation as well as the necessary training to execute it. The transition is part of a brand's evolution from doing social to becoming social.
Understand the Long-Term Vision for Roles
It comes down to evolving to have every player where its strongest and most valuable. The people behind a brand know their consumers and should be the ones developing the relationships with them. It gives them direct access to their customers and gives consumers the ability to connect with the brand easier than it would have been with a third party between them.
On the other side of the coin, it puts agencies where they can be most valuable, being strategic experts and providing guidance on where a brand should go and what it should do to see further success through social media. Let agencies bring the expertise on strategy and marketing tools and brands be the experts on their customers. The balance is a potent combination.