A Cre8asite Forums thread discusses the ramifications of giving out SEO for a fee on a one-time basis rather than having a long-term consulting project. Not all individuals are equipped to handle lengthy engagements nor do they really have the time. Is it worth it, then, to give advice to people who don't know how to manage their sites to explain that their visibility is at a complete minimum?
Absolutely. EGOL explains that he's already done this for some friends. He explains that the service he provides shows that the client websites are invisible in search. He then gives them keywords to optimize for and teaches them how to write for search. They work on the copy, send him an update, and made basic optimization changes (rewrote title tags, removed frames, etc.) With these optimization changes, they got 20 times more traffic than they previously received.
iamlost goes a step further to say that there are two ways you can package this deal. One can be an economy option: you suggest changes, and they'd implement them. The second more full-fledged package would be the gamut: you offer the advice and apply the corrections.
There is a breadth of information in this forum discussion, and I barely scratched the surface with this summary. Please read and engage in the lengthy discussion at Crea8site Forums.