The following refer specifically to consultants in search - people who help other companies get the most out of their search traffic.

Brand Level Experience: While experts generally carry experience with a few Fortune 500s (or 1000s), novices often haven't dealt with a recognizable brand name. The difference is in how to approach projects - with small brands, the biggest struggle is getting recognized by the engines, with big brands, the challenge is more frequently (and sadly) with management.

Holistic Approach: While novices often approach a project with on-page SEO basics, a link building campaign, keyword research and a PPC campaign, experts can identify and diagnose weaknesses in site architecture, customer targeting, usability, design, analytics and dozens of other issues.

Sixth Sense for Rankings: Many experts have what I dub the "ranking sense." They can, in a matter of a few link searches and some competitive analysis determine the scope, difficulty, trends and opportunities of a market, even if they haven't worked in that field before.

Get the full story at SEOmoz