My gf also work for 7-11 but in the city area. this type of customer are normal in the retail or sales line. just because they think customer are always right they think they can do as they please. If we talk back they'll complain. thats why the singapore campaign later mention about "everyone plays a role" it's not easy doing sales in singapore cuz we're too tired and forget about manners sometimes. i've been overseas and i've notice that they're more polite than us even when we just pass by and we never met they will still say "how do you do?". We're still a long way from it. sometimes when staff say thank you, some customer dont even reply. if re;lying is too much to ask than a simple smile will also do
