Then there is the Henry doesn't know what Paul is doing syndrome...In 30 years doing this, i've run into all sorts of characters but as stated above....BE POLITE!
Know your regs is the best. Have any kind of manufacture info handy.
I've had cases where I know the State water code better than what the City inspectors will tell you to do, but it still boils down to you have to follow your local code.
I will be honest about something, sometimes its about putting the money in city coffers than actual safety concerns.