Is Google now a business consultant? Google is now offering advice on how to hire an SEO firm. Of course they have some “Google twists” that are biased towards Google, but overall it is a decent list.
1) Can you show me examples of your previous work and share some success stories?
2) Do you follow the Google Webmaster Guidelines?
3) Do you offer any online marketing services or advice to complement your organic search business?
4) What kind of results do you expect to see, and in what time frame? How do you measure your success?
5) What’s your experience in my industry?
6) What’s your experience in my country/city?
7) What’s your experience developing international sites?
8) What are your most important SEO techniques?
9) How long have you been in business?
10) How can I expect to communicate with you? Will you share with me all the changes you make to my site, and provide detailed information about your recommendations and the reasoning behind them?
If I was to boil it down I think I’d go with this:
1) Can you show me some example clients of yours and share what was successful for them?
2) What is your overall SEO strategy, and where are you most proficient? Do you employ black hat techniques that can get me banned?
3) What do you offer for analytics, web design and usability, conversion tracking, and PPC?
4) What kind of results can I expect, when, and how do I measure success?
5) What’s your experience in local SEO? (if applicable)
Lee at TopRankBlog provides some more detailed discussion on the questions.