Online property portals in Beijing have been forced to remove "illegal information" in an attempt to curb rising prices in the capital.
The sites had until Wednesday to remove ads promising high returns and even good feng shui, state media said.
Beijing's surging home prices have made it unaffordable for many, and led to high debt levels.
Authorities have issued new restrictions this year, calling the property market an economic risk.
This includes raising the minimum down payment on a second home and suspending individual mortgage loans of more than 25 years. Third property purchases and any form of financing advice are also banned.
The crackdown now extends to sales tactics used by online real estate portals, some of which tout "limitless potential for price gains," according to Xinhua.
The Chinese state news agency said 15 property portals, including popular sites Lianjia and I Love My Home, were told to take out posting and claims that broke regulations on property advertisements.
It listed several of these rules, including a ban on "fengshui and other superstitious content", and a ban on "promises of appreciation on investment returns".
Feng shui, which means 'wind' and 'water' in Mandarin, is often consulted when deciding property value.
Xinhua said authorities will begin checking the sites on Thursday.
The world's second-largest economy is widely expected to show slowing growth as the impact of earlier stimulus measures wear off.
The property market contributes to around 20% of China's gross domestic product and there are fears a crash would severely damage the economy.
China releases its first-quarter growth figures next week.