To be really honest, its better to start reading how to do it yourself. There is a lot of smoke and mirrors in SEO. If you do it yourself and learn how to measure it yourself at least if you do buy it in later you can gage its success (or indeed failure).

Just avoid anyone who promises #1 in any search engine, thats normally a sign of black hat SEO which could get you banned from most search engines (Especially Google).

Jen