The ONLY way I consider not being paid for the
SEo and taking a punt is when I am offered a share of the company or when I get an affilliate deal as the main affiliate (IE all the sales go through me as an affiliate at say 10-20% )
I honestly don't see why anyone would just lay down and agree to grant that much credit. That said in the past i HAVE qioted for this sort of work, but charged exactly double my rate for an 'on results' payment. The guy turned around and told me there was no way he was going to pay me twice my rate! His call, I was approached by one of his competitors a month or two afterwards, and they now dominate the SERP's. Oh and they paid me normally

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OWG is old, Bald and Welsh, and provides
Seo From Wales - he also thinks Rugby is the god of sports