Each SEO professional has his/her own strategy to get and keep clients on top of the market, whether he/she works independent or for a company.
However, it seems like some SEO Experts become more "successful" than others, maybe for their reputation as professional or simply the company they work for. That's why I have always asked myself about what really makes an SEO expert "successful":
Is it the top positions obtained?
Is it the top quality links obtained?
Is it the Google PR obtained?
There is no doubt these facts can tell us something about who has been working in SEO strategies, however the people who hire SEO may have another way to "Measure" the success such as a fast investment Return. What I try to say is that the person who hires SEO may not be interested in the work done and only wants to focus in determine how many contacts, sales or reservations his/her website has done during the SEO strategy.
In your case: How do you measure your SEO Success?