There was a post here not to long ago about someone offering SEO services and a slight debate on whether someone should be guaranteeing top positions in google etc...most people know my feelings on that kind of promise....
I think many people can be misinformed when looking for someone who can assess and optimize their site both on and off page and can be easily misguided if they do not understand SEO. Obv if you are looking for someone to do this for you than odds are you dont quite understand all there is to know or at least enough to get you buy. I read this blog faithfully daily and yesterday he wrote an incredible article for people who are thinking or in the process of hiring someone to optimize their sites. Way to many people focus on links, and not enough about the other stuff which in almost all cases is equally or more important.
anyway here is the article and if you are considering hiring someone to do this kind of work for your site(s) I really suggest you read this first, Could mean a world of difference between what kind of person you hire and what you will get for your money
Layman's Guide To Hiring An SEO