Forum marketing is a very powerful marketing technique when used properly.  When used improperly, it can turn off potential buyers and waste your efforts.

Forums are places for the free and open exchange of ideas and information.  You are encouraged to use the forum in such a manner.  Help people, post good helpful information.  In this way you will become known as an expert, people will like you, and be more inclined to buy from you. 

Be very careful to keep your posts helpful and positive.  Never flame or criticize.  If you are negative, you will not be recognized as an expert, rather you will be known as a jerk.  While the Rich Jerk may get away with it, for most of us it is not a profitable reputation.

Now, how does forum marketing benefit you?  First, when you are recognized as an expert, the buying barriers will begin to come down.  Second, you will make good use of your signature line.  After your signature you are usually allowed to include a link to your site.  Through this link your readers will find you and your products. 

Be careful to research and follow the rules of the forum with regards to posting and using your sig file.  There has been a lot of abuse of these rules recently and many forums have established strict rules.  Failure to follow these rules can get you banned from the forum and turn off a lot of  potential customers. 

You must respect the purpose of the forum in the free exchange of information and ideas.  Forums are not meant to be an advertising vehicle for your product, no matter how good it is.  By responding to questions and offering good advice and helpful information, your reputation will grow and you will make more sales because of it.