Why professional guides?
Professional guides always thinking about guiding guest from all over the world and invest themselves. Also they have a lot of experiences to answer your questions and solve problems. So I recommend you to hire a guide holding the government license.
However, I understand it expensive to hire a professional guide every day 🙂
Free volunteer guides
Here is a volunteer guide group organized by Tokyo government.
Tokyo volunteer guides
Your responsibility is paying for transportation, administrations (if any) for yourself and the guide.
Gratuity will be appreciated, I think.