How do you choose a SEO company?

One of my clients, a professional speaker, asked me this question recently:

"I have been emailed by this company [url here] re their services. What's your view on these types of companies? What questions would you recommend I ask to ascertain whether these sorts of services are worth the money?"

I reckon SEO is still worthwhile, though it's just one of the things to do, and becoming less and less important.

I reckon you should ask these questions:

1. What other professional speakers [insert your own industry here] have you worked with?
2. Are clients really looking for speakers using Google?
3. What is the best kind of qualified traffic you’ll get me?
4. What conversion metrics do you use to measure success?

And ... most importantly ... What about the fact that people are using Google less to search by topics?

The person I refer clients to when it comes to SEO is Ed Keay-Smith of www.adwordsmarketing.com.