Offering an SEO-friendly site is a bonus for your clients, especially if you can prove it. I would tend to build this into your cost.
Since there is so much involved with SEO, I wouldn't go down the route of offering it as a service. I would offer strategy guidance and then explain to the client that there is some responsibility on their part, especially on the 'quality content' side of things. You will just tell them how to execute.
You can't just 'hand over' SEO anymore unless you've got a buck-load of money to do it properly.
Just another point.
@webgeek is right about being able to rank highly without building links.
Not wishing to blow my own trumpet but I have a site that
ranks 1st in Google and I've not done
ANY link building. My strategy was to focus:
- Achievable Keywords
- Some Technical SEO
- Quality On-site Content
The result is
3.64% bounce rate for the past 12 months. Clearly, that tells you what you need to be focusing on.
Matt