Is it possible to prove that a hand sanitizer can kill 100% of a person's germs?
There's no realistic way to prove that your hand sanitizer can kill 100% of a person's germs. In fact there's probably no realistic hand sanitizer that can do that. The reason is that there are just so many germs. There are billions of germs on your hands. To compare, there were only a few hundred thousand people in Hiroshima when it was hit by the atomic bomb in 1945, and even that did not reach 100% fatality.

It's because it's hard to kill all germs that antibiotic resistance is a problem.