Rand wrote an interesting post about 10 questions you should ask to determine your value as an SEO. It's a good read, especially the comments.

It's no secret that I've been frequently disappointed by the level of knowledge of many SEO companies, even those who have a big presence in the industry. In fact, I believe that in the current search marketing environment, less than 30% of companies that spend money on organic search ranking services are getting a good deal.

Rand focuses on technical understanding, mostly in Google. He implies that being able to answer the questions makes you a value add provider -- I disagree. There are plenty of people who can answer most, or all, of those question and still not provide value to a customer.

Here is something a little more appropriate for a customer. Ask yourself the following questions:

1. In how many languages can I code a site?
2. Can I do link building?
3. What types of servers can I implement a 301-redirect on?
4. How many ways can I implement a site wide change?
5. What types of analytics can I use?
6. Can I generate valuable insight from analytics?
7. What social media sites do I use?
8. What blogs do you read?
9. What site do i visit?
10. Do I know someone who can do the things I can't?

If you can't answer my 10 questions, it doesn't matter how many of Rand's questions you can answer.

Bringing value to a client is not what you know right now (Rand's questions), but rather, what you can learn (my questions 7- 9), what you can do (1-6), and your dedication to completing the task.