"Sister Fang" seems to be also called "real estate consultant", which refers to the professionals who guide and help customers to make correct purchase decisions, promote real estate sales, and provide investment and real estate professional and consulting services for customers through on-site service in the sales office.
The reason why real estate consultants are called "house sisters" is that on the one hand, they show the affinity of receiving and serving customers, and they are intimate people who invest in real estate, on the other hand, they also affirm their professional ability in the field of real estate investment consulting.