Just know who you are dealing with if you contract a "social media" expert -- and be skeptical of firms that come calling. There are many unscrupulous companies and individuals looking to make a fast buck that will try to "scare you in" to a contract for social networking services with insane retainers and high fees for things you can certainly do yourself.
No matter whom you pick to assist you with social media, just know that largely, it's all free (short of devising a plan and an on-going time commitment) and there are no silver bullets.
Much like SEO, no matter what other vendors tell you, there are no insider-secrets or some magic edge that "firm A" can offer you over someone else. And, there are no guarantees of success if you or someone on your staff cannot make the time commitment to sustain your goals for social media.
The bottom line is: no one knows your business more than you do -- and skipping the shortcuts to a create a meaningful campaign that is forthright, meaningful and connective to your customer audience will go much farther than bringing in a vendor that may ultimately damage your credibility. It's about talking and listening -- that's why it's called "social media".