The OFT said some estate agents were bullying housebuyers into accepting extra financial services, withholding information, or misleading sellers into agreeing contracts they were not obliged to sign up to.
"It is extremely disappointing that some undesirable practices are making a comeback," said John Bridgeman, the director-general of Fair Trading. "Agents should take note that if I have evidence that they are failing to meet their obligations I can ban them from practising," he added.
Mr Bridgeman said he could recommend the Government ban the offering of "linked services" by estate agents if they failed to meet their obligations.
The "undesirable practices" creeping in included:
telling buyers that if they do not take linked financial services, or use the agent to sell their own property, they will not be put on a "preferential service list";
telling buyers that their offer would not be passed on until it has been "qualified" by the agency's financial adviser;
telling sellers that the law requires them to sign agreements with an agent when there is no such obligation;
using "for sale" boards incorrectly.
"Estate agents have a fiduciary duty to do the best for their client. They cannot achieve this if they are only prepared to circulate details of properties to, and forward offers from, a preferred group of buyers," Mr Bridgeman said.