I thought I'd mention the Photo Marketing Association (PMA) http://www.pmai.org
They're a non-profit, primarily aimed at camera stores and photolabs. They provide marketing tips, materials, etc., with a monthly magazine and events.
The use here would be tangental, but they're better than nothing. They have some free info on their site, but most of the stuff you have to buy. I'm a former member, but not in my restoration/retouching capacity.
They do tend to get a little full of themselves, telling you how wonderful their logo will look on your business card and all. Anyone that has heard of them knows it simply means you paid your subscription fee, and anyone that's never heard of them won't be impressed.
But, they do have some good, basic marketing help, specifically designed for those who don't come from a marketing background. The only caveat, as I said, is it isn't precisely for restorers/retouchers.