Personally I think it's very easy to define the phrase SEO and what somebody offering it should be doing. If they are guaranteeing good rankings in a few weeks without some hard work then they - in my opinion - aren't anything to do with true SEO.

For proper rankings you have to research your target market, know your keywords, find similar sites and link with them, one of the most important aspects of any web marketing is your content, if you have great content then people will link with you. Getting quality one-way links from sites that are related to your content will improve your rankings no end, good one-way links are like gold dust. People these days also seem to overlook how well three way linking can work for them, but like most things you have to put in the effort to see the returns.