I find NTUC supermarkets are impressive in customer service.
It's not easy to be a cashier there because you have to say "Thank you" to each and every customer.
Some supermarkets here do not have this culture.
On one occasion, I forgot to take back all my purchases.
I contacted NTUC and when I went back to the supermarket, they were returned to me. They have a proper system for such eventualities.
On another occasion, the customer in front of me stole my plastic bag of stuff right under the nose of the cashier when I was chatting with a friend. The cashier was annoyed at the theft(not a mistake certainly). Anyway, she told me to get the similar items from the shelves as replacement. I was glad to see that NTUC cashiers are empowered to take the necessary action in such an eventuality.
That's why NTUC is always packed with customers-due to its good customer service apart from its fair prices.