In life, we almost never wait for 100% guarantees.
We trust that the dentist is a dentist, the taxi driver is a taxi driver, and so on—and put our lives in their hands—on flimsy, tacit evidence.
Yet, when it comes to a simple good deed, people demand 100% proof that this is really what G‑d wants them to do!

Good analogy. We don't blindly trust humans with our bodies, and we shouldn't blindly trust G-d with the world. Don't trust that the dentist is a dentist. There have been cases of fake doctors practicing without a license. Check your state licensing board's website.
The analogy in this Daily Dose does bring up another point.
Taxi drivers, dentists, even someone who just braids hair, need licenses from the government.
We don't trust that they are good; we make them undergo training and pass tests. We have boards to certify them, and to suspend them if they kill even one person.
Yet, we trust G-d with far more, with no certification or licensing, and no board suspends G-d when G-d kills millions.
The FDA won't allow a new drug on the market until it is demonstrated to be safe and effective, usually in a double-blind clinical trial. Marketing a medicine or medical device as a way to cure or prevent disease based solely on our "faith" that it will work isn't just dangerous; it's against the law.
Yet, we have no problem saying to have faith in G-d without the same level of rigorous testing.