What are Some Questions to Ask an SEO Firm to Check their Legitimacy?

If you were interviewing an SEO firm to see if they're for real, what questions would you ask them? A High Rankings Forum thread touches upon some of the must-know questions, and they're outlined below:

1. How long they have been doing SEO?
2. Can you give me three clients that you have had first-page results for?
3. What are some campaigns you have succeeded with?
4. Can you illustrate any significant traffic boosts or conversion boosts?
5. What is your general SEO process?
6. What is your criteria for choosing keyword phrases?
7. How is success measured?
8. What should you expect from us as a client?

And the list goes on and on. What would you add to this for desired results?

Forum discussion continues at High Rankings Forum.