The person who remembers your courtesy may return long after forgetting the exact price.

Prices are forgotten quickly and treatment is not. People remember the shop that took the return without fuss, the workman who explained rather than sighed, the person who held a door on a bad day. That memory outlasts the transaction and shows up years later as a recommendation or a return visit nobody could have forecast.

Be decent in the moments carrying no obvious return: the small refund, the extra explanation, the courtesy to someone who is never coming back. Do not keep accounts on it. Ordinary kindness has a long and unpredictable settlement date.