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This is a bit of a catch 22... The overall benefit of SEO will vary from site to site, the only way to prove it will work on your clients site is to do it! Explain to them that optimising the content will not only improve SEO rankings but also help with converting users from others sources. This is because ultimately SEO is all about optimising your sites for user experience. Optimised content = better user experience = more conversions = better search engine ranking! Steve