If true, where were all the people from the handball court? This was an event YOU paid to have, had all your equipment there (with problems) and barely any traffic. As I recall, people from here (and passerby's) actually did show up and question the sound (and actually heard it go off).
Additionally, people don't generally complain about sound directly to you. They just won't ask you to come back or refer you (the person hiring you is not who I'm referring to).
What I've learned from this thread:
Step 1: Forget about what you sound or look like
Step 2: Forget about ethics and don't waste time looking for profitable events and growth. Instead, find someone that gets money from the city and other donors - this is all money for you
Step 3: Offer this person services for 'x' - but don't tell them it's basic services or that you have more equipment
Step 4: If it's for a charity or good cause .. like cancer, aids, recovering alcoholics or drug abusers, veterans, people with disabilities, etc - charge them 1-10,000% more than a normal event
Step 5: When they ask for more, tell them it's extra - but watch out for them trying to get it for nothing - and don't tell them you have even more stuff
Step 6. Tell everyone that the event could be through the roof if the client lets you use more equipment - but watch out for them trying to get it for nothing
Step 7: When there are problems or it doesn't sound or look good, blame someone or something else
Step 8: Unless people are complaining to you, then there are no complaints .. and you're a rock star
Step 9: Raise your prices before the next event, just for the heck of it