Here are a couple of articles that relate to selling timber from the Alabama extrension service website. Even though it is an Alabama publication I think the general principles would apply anywhere. Your own state extension service may be able to provide more specific information.
A guide to selling timber...
Timber sale and harvesting contracts...
I can tell you from experience that there are a lot of timber buyers that rely on inexperienced sellers to make their profits. They are not all like this but it just takes a few bad apples. Some things they might do include:
-Paying you less than the timber is worth (ie buying sawtimber at a pulpwood price)
-Cut an area larger than you wanted. A timber harvest should be clearly marked with paint.
-Slip across the property line and cut some of your neighbors timber
-Work in really wet weather and destroy the site quality
-Not carry sufficient insurance.
-Promise to put up gates or restore roads before they leave and then split without fixing any problems.
-Work on their equipment and let the oil and hydraulic fluid pour on the ground.
-Leave litter everywhere or bury it somewhere.
-Use tree tops to make a creek crossing or even worse haul trees down a wet weather creek bed
-Work without a contract and take virtually forever to finish the job. You become the backup wood supply that they can turn too when they have no other wood to cut.
I am not trying to scare you but I have seen all of these thing happen at one time or another.
The advice from others to hire a consulting forester is the best you will get if your land and how it will look afterwords is important to you. He/she will know everyone in the area who buys timber and what their habits are. The forester is their to protect your interests and will likely more than pay for themselves in the long run.