I have a feeling that if the FAA wanted you to be schooling their inspectors on how to do their jobs, they would have put you on the payroll.
That's really irrelevant.
An inspector at the FSDO level has no authority to interpret the regulation. If you obtain a letter from the local FSDO that tells you that you can do something, it offers no protection if the advice is wrong. You'll often hear people say "get it in writing," but even in writing from the FSDO level, the counsel you may receive offers no legal defense. You can't find yourself in violation, for example, and say "Inspector XXX told me it was okay. Here's the letter." That just won't fly.
Inspectors are known to be wildly wrong in some cases. I've met a number of inspectors with a very poor understanding of the regulation. It's part of the reason that we have legal interpretations and other means of understanding the regulation. The person charged with the regulation, it's maintenance and interpretation, and administration of the program is the FAA Administrator. The Administrator designates certain offices and personnel to provide interpretations of the regulation, and these are the Chief Legal Counsel and Regional legal counsel. Those letters and interpretations are defensible in administrative court, before an ALJ.
What one inspector tells you at one FSDO may be unacceptable to an inspector at another FSDO. Pilots have suffered enforcement action in the past when working off what they were told by one inspector, only to be busted by another. A statement by an inspector isn't a defense, even if in writing. The inspector doesn't have the authority to interpret the regulation, and ignorance of the regulation isn't a defense.
Your assertion that one has no business telling the FAA how to conduct it's business is utterly wrong. Most certainly we do. I've seen a lot of unrighteous dominion taking place by inspectors in the past; people who let a little authority go to their heads. We all remember the Bob Hoover saga, and there are numerous cases out there involving attempted enforcement action by inspectors that's struck down; the FAA loses all the time. Simply because an inspector says this or that doesn't make it so, and most certainly we should not simply lay down and roll over because we are told something by an inspector.
I've known some very good personnel working for the FAA, but I've known a lot more who are only there because they couldn't make it in the private industry. I know one individual, for example, who is presently an inspector who has wrecked or damaged numerous airplanes. Another who was fired by an operator for whom I worked, and moved on to another where he was fired, both times for nearly killing people. He's now an inspector, and one of the biggest idiots I've ever met in the business. This doesn't make a ringing indictment on the FAA nor on individual inspectors, but certainly don't ever take a Form 110a and an inspector credential as a statement of anything but employment.
Inspectors can initiate enforcement action; they cannot provide a legally binding interpretation of the regulation, nor issue statements of policy on behalf of the Administrator.