Questions 1 and 2
What do you know about social that I don't?
Everyone thinks they know social, but the right partner doesn't just know social, they understand your broader business goals. The right social partner will work with you to define success both strategically and tactically in the context of your broader marketing goals. The right partner will value investing in growing and engaging with your community to meet your marketing, customer acquisition, and PR goals. Social marketing vendors who narrowly define social media success by the number of fans you can amass on your Facebook page are missing the point. Social isn't just about getting the "like" -- it's about long-term engagement and the conversion of likes into actions.
OK, let's get down to business. How do you measure social media ROI? (My boss will ask.)
The right partner will measure your investment in social marketing against your overall goals (not just in a silo). This partner will provide integrated metrics tied to an overall value of an engaged community member. Analytics shouldn't just focus on fan growth -- they must offer insight into the overall health of your Facebook and/or Twitter community, metrics around the key drivers of engagement (these drivers include polls, promotions, sweepstakes, etc.), and metrics on the tangible impact of that engagement on your business goals (such as uplift on email, ecommerce, online reviews, etc.). Measuring social ROI can be complicated, but return on engagement is something that can be measured, so make sure that you ask your vendor the right questions about how they approach it.
