I've been working for a search engine optomization company for many years now. I still see the whole process offered by many companies as a little bit shady.

At the end of the day, nobody can make a search engine do what ever they want. You can't pay google to move you up higher in the rankings, nor can you know exactly how they work. In this way SEO is always experimental, so beware of any company that guarantee top 10 rankings. They cannot guarantee anything that they are not in full control over, if your site can move to front page searches in a matter of weeks then it's likely that you can do it yourself with little time and effort.