Respectful Greetings

A regular Vietnamese customer always bows slightly and addresses the female staff as "madam". When visiting Thailand on a holiday I was greeted everyday with the same respect and a slight bow with the words "Sa wut dee kah" (hello, how are you). Upon returning back to work this customer had noticed my absence and I explained I was on holiday in Thailand. He lived there for a few years and asked it I knew Sa wut dee kah - I said yes. So everytime he comes in the door and I am on desk we make eye contact and slightly bow saying Sa wud dee kah. It is a pleasure to see this gentleman come in to the library with his wife and grandchildren.