It's not the customers mistake ... when has a restaurant ever let you type in your own amount? The Cashier would have typed the amount and the customer probably did not notice the extra 0 when entering the PIN.
Still ... good on the restaurant for trying to fix it.
Those senior folk with aging knees and hips can not manage the stairs in many cases. I don't know what the best answer is ... certainly lifts or elevators would be way to expensive.
They need to get rid of the afternoon sales ban (from 7-11 etc) as well ... that never made any sense. Last time I was in Chiang Mai, even bars were not allowed to sell in the afternoon ...