In Vietnam, it is customary to say "thank you" in response to someone doing something for you. This is especially common in the service industry, where workers are often expected to show appreciation for tips or other forms of gratuity. Saying "thank you" is a way of acknowledging that you have received a service and are satisfied with it. It is not uncommon for foreigners to be unaware of this custom, and as a result, they may not say "thank you" when they should. This can be seen as rude or ungrateful, so it is important to be aware of the proper etiquette. When you are the recipient of a service, take a moment to say "thank you" to the person who provided it. This is a small gesture that will go a long way in making a good impression and showing your appreciation.
In Vietnam, it is customary to say "thank you" in response to someone doing something for you, regardless of whether it is a service or a gift. The most common way to say "thank you" in Vietnamese is "cám ơn", which is pronounced "gam on".
Thank you for your service!