Shonky businesses were taking advantage of residents because most did not know how the scheme works.

Rodney Griffin from Rafter Insulation said many home-owners in the north-west who applied for the Federal Government's Energy Efficient Homes Package, which includes $1600 for ceiling insulation, were unaware there were no upfront costs.

He said many residents were sceptical about the Government's program and were suspicious of ``why they were getting something for nothing'' and asked ``where is the trick?''.

``About 30 per cent of callers already have insulation and want to upgrade, but can only do this if they have minimal thermal rating,'' Mr Griffin said.

``Others are tenants who don't realise that they can also apply if they have the written approval of their landlord.''

His business has increased since the first stage of the program was announced in February, with almost all new customers referred by existing clients.

Mr Griffin said this was a testament to the company's reputation and the trustworthiness and reliability of his employees.

``With every job we conduct a physical inspection of the roof cavity, measure the house and then work out the quote accordingly.''

He warned residents should not give deposits for any type of work and should ensure insulators physically inspected the house before giving quotes.

Environment Minister Peter Garrett said the 100 de-registered companies (56 in NSW) were a small percentage of the 7664 installers registered under the scheme.

He said complaints of faulty installations amounted to less than half of one per cent of all 370,000 installations, which cost more than $500 million.

Mr Garrett refused to name the deregistered companies but residents can check for their insulators on: www.environment.gov.au/energyeffi ciency/insulation/index.html.

< p>