My mom has a regular vendor at the vegetable market, Old Wang who sells vegetables. She always buys from him and never switches.

I asked her why, and she said Old Wang is honest and the scale is accurate.
One day, my mom asked me to help buy vegetables, so I went to Old Wang's stall, picked a few items, and after weighing, Old Wang said: "Total is 52, just give 50."
I scanned the code and paid 52.
Old Wang was stunned for a moment and said: "Young man, I said just give 50."