quotation marks intended http://outspokenmedia.com/seo/google-profiles-seo-as-criminals/ interesting reading.
Because it's kind of the truth. Regardless of what you think, there is no common accreditation for SEO. This means anyone can claim they are professional and also "claim" they've gotten results. I think the best way to do SEO is to do it yourself, for your personal websites or businesses, using a company can be a waste of money if you use the wrong one.
Profiling doesn't happen as often as you would think. Do a search for "seo service" and you will find a website that is, defined in Google's own words (from a tutorial somewhere), a company you would not want to trust because they offer guaranteed rankings: http://www.rankpay.com/ Where's the justice there? I think the average SEO company doesn't have a thing to worry about.
I tried an seo company once and I was able to a better job my self. They spammed my site all over the place.
A good manager is someone that can use their professionals efficiently and not necessarily have to be the one to do all of the work themselves. If you have no clue about SEO and do not want to research it, then hiring a reputable consultant to advise you is best. This way You, the person that makes the decisions for your site, learn what is involved in it all. You are then knowledgeable enough to screen an SEO company for doing the leg work.