[StockHuman]

In addition to other responses, know that the zero-note makes its way to the corrupt official's hands before they can inspect it. From their perspective, they've just completed an illegal act with someone willing to challenge their authority out of a sense of justice. What would you even do after receiving a zero note instead of a bribe as requested? So goes the example: of a smile and nothing more.

[alwa]

But in cases where the bribe is to expedite an official act—they give the example of getting a driver license issued—why wouldn’t the official just give the smile then shuffle your application to the bottom of the pile?

[dotnet00]

The official would be wary of appearing to take retaliatory action, since by being given the note, the person would have already signalled that they are the type to actively oppose bribery rather than just refusing to pay and otherwise turning a blind eye.