A former Sydney real estate agent has lifted the lid on the industry's bag of dirty tricks, warning homeowners they could be tens of thousands of dollars worse off by trusting the wrong agent.

From inflated price promises used to win listings to 'dummy offers' designed to wear sellers down, former real estate agent turned consumer advocate Neil Jenman claims many Australians are being quietly short-changed at every stage of the sales process.

He says the tactics don't stop there. Sky-high commissions and even open homes, he alleges, often work in the agent's favour rather than the seller's.

'The real estate industry is rife with crookedness,' he told the Daily Mail.

Mr Jenman claims one of the most common traps is agents quoting overly ambitious sale prices to secure a listing, only to later condition vendors into accepting far less once they are financially committed.

Mr Jenman alleges agents use open homes to harvest future clients rather than maximise the sale outcome.

'The worst thing you can do as an agent at an open inspection is sell the property,' he said.

'If you sell it too quickly, you lose all the extra leads like neighbours and potential future clients who come through to see what's happening in the area.'

In another controversial tactic, Mr Jenman said some agencies use deliberately low initial offers to 'soften up' vendors and reset their expectations.

He recalled interviewing an agent who claimed staff were instructed to present an offer around 20 per cent below the asking price after the first open home.

'It softens them up,' he said.

He warned the approach could leave vulnerable sellers, including elderly couples, significantly out of pocket.

'They might be promised $3 million, only to realise later the home won't sell for much more than $2.2 million or $2.3 million,' he said.

Mr Jenman warned commission rates have quietly crept higher since deregulation and believes sellers should negotiate agents down from around 2.5 per cent to as low as 0.5 per cent.

Real Estate Institute of Australia president Jacob Caine said it was a 'lazy and unfair smear' on an industry made up overwhelmingly of honest, hardworking professionals.

'Where agents break the law, they should be investigated and punished. But attacking an entire profession in this way is simply wrong,' he said.