"I read HN every day,I read the comments, and I understand the culture here. I was thinking I could give something back to the community by answering some questions."

why don't aswer to questions on HN instead of use e-mail? isn't "community" to share with all SEO tips?

"SEO must find the correct keywords for a site not the client"

part of SEO job is to find the correct keywords for a site and optimize for those, no? but you say "I need: The URL of the website; some keywords"

In conclusion i'm work every day with SEO/SEM and in this sector the word "free" is used often for ulterior motives, hence my doubts...why a pro SEO should work for free?(work is time and time is money)...all here.

Have a nice day ;)