http://www.google.com/webmasters/seo.html
"Make sure you're protected legally.
For your own safety, you should insist on a full and unconditional money-back guarantee. Don't be afraid to request a refund if you are unsatisfied for any reason, or if your SEO's actions causes your domain to be removed from a search engine's index. Make sure you have a contract in writing that includes pricing. The contract should also require the SEO to stay within the guidelines recommended by each search engine for site inclusion.
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