The guy that runs the closest LFS to me has no interest in servicing tanks. He gladly gives those who inquire the name of a guy that will do it. Great advertising for "that guy". The moral of the story for anyone interested in this line of work is to talk to everyone that sells fish and pet supplies. Give them business cards to hand out.
And another word of advice from years of service experience...have a written "agreement" (customers hate the word "contract"). In it state that death is a part of the cycle of life and all fish will die...and that you will not be responsible for replacing them. Same thing for equipment. Nothing lasts forever and everything will break. The most stressful time for equipment is during its maintenance and that is when it will break. Most things will break while you are working on it. Many people translate this as "you broke it". Guess who they expect to pay to fix it. Make sure your written agreement has a statement about this so there are no hard feelings later.