Great article in Search Engine Watch, “How Do You Find High-Quality SEO Services?“:

Because anyone can sell SEO without a license (or sadly, without any knowledge), the industry is rife with, frankly, crap.
Coupled with this reality is the fact that SEO is a combination of art and science….
High-quality SEO is in high demand indeed. There’s a lot of money at stake, too. Traffic and ranking improvements can mean millions of dollars for a company’s bottom-line revenues.
This has created a market with service providers who are adept at selling SEO services, but less skilled at carrying them out.

The man speaks Truth. Read the whole article.