Estate agents who willfully underquote houses going to auction will apparently get big fines with a new investigation. It won't be hard for them to find examples. Say, a 2-bedroom house quoted as "over $500,000" in an area which hasn't seen a house sale under $560,000 in the last six months. The real classics are the ones where the reserve price is higher than the price quoted as the guide price.
The Office of Fair Trading is going to have trouble though, as agents can easily point to "market factors" being responsible for their errors. In a soaring or crashing market, this could well be true. What's more, if an individual property captures the hearts of a few people, it could well go for much more than its market worth.
I have a quick and easy solution. The agents have to quote a price to the sellers. Force them to publish that price whenever they advertise the property. Then third parties can keep a league table of the agents: how close their estimates were. That will keep the bastards honest!