Dan, I have being what I do for 4 years now and have consistently landed businesses in the top 10 rankings for their relevant search terms, often in rather competitive markets.

I see little need to charge maintenance fees because if the site is well optimised in the first place their is little else to do and their presence snowballs and grows and becomes stronger as time goes on.

I'm not talking about techniques that are tricky at best and would need continual tweaking to stay ahead of the algos.. I am talking about on-site optimisation intended for long term positioning.. maybe there is a difference in what is offered and what is meant by "seo"? :)