Did you know that choosing an SEO can make or break your company? The Google Penguin updates (battling unnatural links) are a good example of this.
Some companies got hit so hard by Penguin, that they actually needed to fire people or even worse, they went bankrupt.
A good example of this is the SEO horror story of Pete Walter from Deal with the Media who almost went bankrupt because of Google Penguin.
So think twice before you hire an SEO. SEO is risky business. If you need help selecting a good SEO I would recommend you to watch Googles video: How to hire an SEO