ken_b - 2:28 pm on Mar 18, 2010 (gmt 0)
I sure wouldn't use a competitor as an SEO.
Why would they use their best skills and knowledge on your site when they could use them on their own site.
A really good SEO firm probably has enough potential customers that they can choose just one from each industry or niche and not have to worry about conflict of interest issues, let alone compete with their customers.
I doubt Pepsi and Coke use the same ad agency at the same time.