Just found an interesting article on SEO, and if it's worth it to outsource your internet marketing.
I'd say for most businesses the answer to this question is the same as it is with your site in general, your computer support, your legal advice, your accounting, and so on. Most small businesses are great at their core competency, whether it's creating art, re-modeling houses, or selling aftermarket accessories. As a former small business owner, I understand the 'I can do it' attitude that many owners take with everything. "I can do the books, I can do the website, I can do the marketing". The real issue arises at the point where you physically can't do it. I used to to tell my computer support customers: "You can take 4 hours out of your day to try to fix that problem, or I can have it done in an hour or less".
So how much is your time worth? That's the real question when it comes to outsourcing. Many times it's often more economical to outsource this type of specialized work. Sure, the owner can (and should) be involved in the process, and hopefully will be empowered to 'tweak' when necessary, but just like I don't write my own insurance policy - experts are great at what they do.
This is a great article that relates specifically to SEO, but the same principles can be applied to any specialized service. Give it a view:
The Big, Bad List of Pre-SEO Questions You Need to Answer, Part I