To be completely honest, six sigma consultants do a much better job than most in house process professionals. And of course they should know a lot because it is their job to do so. Which is why so many companies nowadays have decided that it is a much better thing to outsource a six sigma consultant for their many projects instead of relying on their own folk to do the work. Additionally, if you get the expert from an outside source then your own men can have more time to focus on their more important tasks.
Six sigma consultants have very strong skills in communication, both written and verbal. Aside from knowing how to be analytical and how to problem solve, these experts combined with their excellent communicational skills have a higher chance of creating successful implementations over those who do not possess the same skills. Another reason is that company employees may show some bias over some projects. If you implement quality in your organization, you will need to create changes that will have profound implications on the way compensation is dispensed and your organizational structure is created. An outsourced six sigma expert will approach the problem without nary a bias in his mind, since he knows that he has no reason to be biased in a company he does not feel any loyalty strings attached to and will thus have no ulterior motives. As uncomfortable as it may sound, it is also quite easier to pinpoint faults at the outsourced six sigma specialist. He can easily acknowledge his mistakes and remedy the problem without feeling like he let down a few close people who might not treat him in the same way.