Contact your lawyer. Contact you professional associations and report these individual for unprofessional conduct. Follow up the junk E mail postings of your customers. This is an opossums for your business to obtain greater market share and to build your on line reputation. Send a copy of your lawyers letter to both the customer and to the offending company.
People like to do business with people who look after their interests.
If you find a spam in a usenet group - take a leadership role. Post information on how to use a cancelbot and forward a copy of your posting to the Internet Blacklist. Remember these companies and persons are attempting rob your pockets and future by destroy the value of the Internet and its marketing potential. By being a good citizen and defender of the Internet you will win the respect, admiration and business of member of the Internet community as well as protecting your own business. Always make use of this type of opportunity as it will lead to increased revenue and a good reason to highlight your business to your target market.