Just Do It
Some international courtesies apply. We were socialized to open doors for others, assist the elderly across streets, pull ladies’ chairs out for their dates, and say thank you for these nice acts in the United States. All of these duties are expected in South Korea.
Don’t expect a “thank you” in return when you do nice things for others in Korea. Why should you get congratulated for having good etiquette? You may believe that the locals are being ungrateful when you open the door for them and don’t receive any thanks. Their lack of response is quite acceptable.