MediaPost: How To Spot A Fraudulent SEO Firm

Looks at the different forms of search engine spamming and what affects they could have on your rankings. According to the article, the 5 major forms of fraudulent SEO include:

Shadow domains: production of multiple websites by using several different domain names to artificially boost search results for one Web site.
Doorway pages: duplicating similar content on several pages in an attempt to expand keywords and drive traffic.

Invisible text: writing text in the same color as a website’s background.
Link farms: creating links to a site from irrelevant or illegitimate “affiliates.”
Cloaking: showing a web surfer one version of a page while showing a search engine a completely different page for its index.

As a result of these techniques, “legitimate companies are getting bumped from Google and Yahoo! for illegal search engine optimization (SEO) practices, and most don’t know why.