Returning extra change nobody would notice is a small moment that tells you exactly who you are.

Handing back money nobody would have missed is a test with no audience, which is precisely what makes it informative. Character is not what you do when the choice is watched and recorded. It is the automatic move at a counter when nobody is looking, and that move gets built out of hundreds of earlier ones exactly like it.

Watch for a small honesty test this week, since there is nearly always one. Give back the change, own the mistake, correct the grade that came out too high. Low stakes, real practice.