One thing that drives me nuts about "so-called" social media optimization experts is there lack of understanding of search terms. It makes me want to scream and pull my hair. Ok, so that aside, do you understand why and how?
Twitter is the easiest and simplest, thus if you are going to hire an SMO expert see if they know how to utilize Twitter first! This is completely hypothetical. Let's say for example you are a plumber and you work in Cincinnati. Your goal is fit keywords and search terms into your conversation (e.g. Cincinnati plumbing, toilet clog in Cincinnati, plumbing help Cincinnati, etc). So this isn't exactly as easy as it sounds because you still need to consider advertising while participating in a conversation all the while making it sound conversational. Takes time and work but it can been done!
The more keywords you have on your Twitter feed the better optimized your page is BUT don't stuff your page to where it seems like your advertising. You will then lose your credibility and personality and you will look too much like a business trying to sell, sell, sell.