Depending on how they introduced themselves to you when they first met you, if they or their assistant said this is Mr Lee, you say Lee lao ban, ne hao, in other words, Lee Proprietor (proprietor of this business/enterprise), how are you? Lao ban is "Boss", and "ne hao" is how are you. He would probably nod to acknowledge you. If it is a manager, you say Lee ging li, ne hao, and "ging li" means manager. If it is not a manager, but senior to you anyway, you say "Lee sin sang, ne hao", and sin sang means "Mr", or "Lee sui jhair", and sui jhair, means Miss, you don't pronounce Mrs as you would then need to know her husband's surname etc. They are very reserved, if the business is quite large etc, so no folksy calling them by their first names etc.
