I was in a 7/11 recently and the till wasn't working and they had to use calculators to add up how much it cost , I put my four beers and bottle of water on the counter and said to her 270 Baht , so did the calculations on her calculator and shook her head and said "No, 230 Baht" .
I smiled at her and gave her 500 Baht , she again did the calculations and gave me 270 Baht in change