http://www.maconline.org/tech/design/fireplace1/fireplace1.html
http://www.gobrick.com/BIA/technotes/technote.htm
http://www.gobrick.com/BIA/technotes/technote.htm
I have seen your stuff posted and checked out your website before. Not a doubt in my mind you can add this to your services offered.
Lots of chimneys need work, most of it is hard to get at and there is a certain amount of liability to be concerned with when you start replacing liners and such. That all leads up to not a lot of contractors willing to work on existing stuff and usually a pretty good profit margin.
Flashing detail at the roof line is a big source of water leaks. Once the brick start failing on the outside, the inside is usually gone also. often the damage is limited to above the roof line, because the higher room temps of attic and house along with less weather exposure means less freeze/thaw cycles and less damage.
Always use cement for a wash and try to sell a maintenance program of inspection and sealing on a regular basis. Can be a steady supply of business if you get a name for it.
I think working with a sweep would be a great idea as they can give a certificate of safety and a video of the inside and you can maintain the outside. Just get one that doesn't want to compete with you for the repairs.
I been taking lots of pics this year, I can give you an idea what you can expect when you open one up. (no pics of the one that was home to about 5,000 bats though. That was nasty...)