Estate agents in Oxford have blamed unscrupulous firms for giving the industry a bad name after a consumer magazine described property valuations as a lottery.

Researchers for Which? posed as sellers and invited three unknown estate agents in Oxfordshire to value a five-bedroom house. Valuations varied from £290,000 to £340,000 -- a 17 per cent difference.

Listing the wildly different estimates by 56 agents for 14 homes across the country, Which? warned that overvaluing a property to get business was a common problem in the industry. It said other agents would undervalue homes in order to get a quick sale.

In six cases, the Which? researchers found the top valuation was at least 25 per cent higher than the lowest, while in one case it was 63 per cent more.

George Stevens, regional director of Allen & Harris, said: "A good quality estate agent does abide by the ombudsman's rules.

"Our staff look at three kinds of comparable evidence -- they research the property, they look at what price similar properties are selling for and what price nearby properties have sold for.

"There's no excuse for estate agents providing valuations that are not accurate."

Giles Lawton, of Savills in Oxford, said: "There are probably some unscrupulous agents who manipulate valuations.

"The problem is, it's impossible to be absolutely dogmatic about house prices. You don't really know until a property is actually on the market."

Wayne Keenan, of Andrews, said: "A good estate agent should always supply details of properties that have recently sold in order to demonstrate the basis of their valuation.

"Reputable estate agents only allow members of staff with a proven track record and an intimate knowledge of the area to go out and value homes."

He added: "It is always up to the seller what price they put their property on the market for, and most agents will help this process by presenting the seller with a range of prices."

The author of the report, Pete Tynan, said: "Some agents give high valuations to get a customer's business, then suggest a more realistic price once they've locked sellers into a contract," he added.

The group is calling for industry regulations and a proper system of redress.

Bill McClintock, chairman of the Ombudsman for Estate Agents' board, said: "The criticism by Which? portrays a fundamental misunderstanding of what an ombudsman scheme is all about.

"It is not set up to punish erring estate agents but so unresolved disputes can be referred to an independent third party for settlement."