The wait staff working in a Chinese buffet restaurant in the United States can basically keep their mouths shut, except for the cashier who needs to speak a few words of English, and the wait staff who collects the plates, paints the tables, and refills the dishes. If someone greets you, you can politely ask:

How may I help you?

After the diner asks a question, you say:

Sure, (and then answer the question).

After the guest thanks you, you say:

No problem or You're welcome!

Don't strike up a conversation with a guest that interferes with other people's meals.