This is a big area in most cases, and it is where most of the creosote both forms during use, and settles after he swept the actual chimney down. It's true, the damper on many fireplaces can be removed so that you can easily get into the smoke chamber for a good cleaning. But this takes time, and trouble, and con-men don't like to spend either. It's VERY important to clean the smoke chamber for this reason alone. Clean chimneys don't burn.
Clean chimneys stink less.
This is a typical scam. Find someone you're comfortable with, and hire him. The crook may or may not be a member of the Guild - either way the complaint can be filed there. Also draft a letter clearly explaining the situation and crooks involved, and send it to the National Chimney Sweep Guild at 16201 Industrial Drive, Suite 8, Gaithersburg, MD 20877. In the past, with all of these organizations and regulators, the response is to file the complaint on record, and that's about it.