One general scam is the construction of "shadow" domains that conduit users to a site by using deceptive redirect. These shadow domains often will be owned by the SEO who claims to be operational on a client's behalf. On the other hand, if the association sours, the SEO may point the domain to poles apart sites, or even to a competitor's domain. If that happens, the client has paid to develop a contending site owned totally by the SEO.
Another illegitimate practice is to place "doorway" pages overloaded with keywords on the client's site somewhere. The SEO promises this will make the page more appropriate for more queries. This is essentially false since individual pages are hardly ever relevant for a large range of keywords. More sinister however, is that these doorway pages often enclose hidden links to the SEO's other clients as well. Such doorway pages consume away the link popularity of a site and route it to the SEO and its other clients, which may contain sites with sleazy or prohibited content.
