Just to be clear, these techniques aren't the only ways negative SEO can be done, nor is it always done to effect a competitor. Some SEO firms have started promoting a "new" form of negative SEO, euphemistically termed "reputation management."
SEO services include the 100% money refund because the website may not be ranked with top search engines like Google and Yahoo, and they refund the money. Therefore, the SEO companies ensure the clients that the money refund will be done, since the search engine optimization experts are not sure whether the site will be ranked with the top search engines.