When offering a service, whatever it is, (and this is a service), two things need to be considered by the individual offering the service: #1 - the customer calls the shots. Still trying to drill that into the head of a very stubborn 42 year railroader I work with (My business partner/Dad). You need to be willing to do whatever it takes to make them happy. If it costs you a little of your profits every now and then, fine. Remember, if you do a good job, they'll tell people. If you do a lousy job (customer service included), they'll tell EVERYBODY. And you're toast at that point. #2- The quality of the work that you do is irrelevant if customer service is bad. Customer Service is every bit as important (if not more so) than the quality of work. How you handle people in the way you talk to them, the way you carry yourself and your ethics is paramount to success. Respect for yourself and others must be given before it is received.
Trying to convince teenagers of this is like trying to nail Jello to the wall. More often than not, it is lost on that generation, I gave up on it long ago, so my advice to you is to heed the good advice that others have provided you with here, and do your absolute best to come across like an adult and your age will cease to matter to potential customers. Act like a teenager though and you'll get nowhere.