I have been hearing this word 수고했어요 instead of 감사합니다 (thank you) after koreans pay at the cashier or after people did something for them. It sort of means thank you for your hard work and is like "辛苦了" in chinese.

I had an interview with cyberoro last week and to be sure of this word  수고했어요, I asked him when and why korean use this instead of the normal thank you. And he told me it means thank you for your hard word and please work harder. I burst into laughter immediately when I heard that but he was not joking at all. He even told me there was a movement to stop people from using this word because it sounds rude. Hahaha, can you imagine you are the cashier and the customer tells you, you worked hard, please work harder. Hahaha!!