Please also see What does an SEO Agency Do as that will also answer this.
A good SEO agency will largely eliminate the random and bring focussed order to your online content.
To do this a good SEO agency has to get you involved. it can’t be done without you.
A good SEO agency will also..
- .. focus your online messaging and brand regardless of the size of your business.
- .. not bamboozle you with 50+ pages of stats, graphs and terminology. It shouldn’t be about them.
- .. give you realistic goals. There is little point in implementing an SEO strategy when there are no resources available to physically do the work.