[Huliwang]

Come to think of it, beer ladies job is like those bar girls in the sixties or seventies working in bars like Sin Popo where horny men went to drink and chit chat with these bar girls. 
What those bar girls did was bring beers and drinks for the men and sit with them for while and then moved to the next table and all the other tables where beers were sered by them. Their pay was very little and also gets comission on the number of bottles they served. Their main income comes from tips and the ang-pai bar girl can get a few hundred in tips per night. Some went out for midnight supper and other activities to earn more. 
The beer ladies in kopi tiam are basically doing and earning the same.