There are concerns over lack of regulation for meth-testing and cleaning businesses - and Consumer NZ has labelled the sector as a whole a ''cowboy industry developed around people's fear''.

Property experts in Rotorua and the wider Bay of Plenty have raised concerns over the lack of standards and training for testing and clean-up operators. One expert estimates there could be dozens of rogue operators across the country.

A new national standard around P-contamination testing and clean-up is expected to be introduced next month but it would be voluntary. However, the Government has plans to make the standard law in future.

Rotorua First National principal Ann Crossley said she was concerned by the lack of control or standards.

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"There is no proper standard at all with the training of the testers very loose. The number of tests out there continue to increase and they are all over the place.

"Just recently we had one house tested and the initial test came back with a positive reading of .99 but when we did the room by room tests, one room came back 1.9 and another 2.61. There's huge variance.

"Then when you have the companies that offer both the testing and clean-up - there's clearly a conflict of interest."

Ms Crossley said landlords would be faced with paying higher premiums because insurance companies were hit with clean-up costs.

"It's just another cost for landlords that will be reflected in rental prices."

Rotorua Rentals owner Richard Evans said he had not seen any evidence of "monkeys" in the industry but had heard about companies making mistakes.

"I heard one story of a house being tested that came back with extremely high levels of contamination. The homeowners didn't buy that so got it re-tested and the results were well below. Turned out the first company had used the same swab stick and liquid to test all the rooms," he said.

"I suspect there are a lot of stories like that.

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"There's just not the regulations there to stop any Tom, Dick and Harry from paying a few bucks, buying the $10 tests and then charging home owners hundreds of dollars to be tested."

Mr Evans said Rotorua Rentals only used two reputable testing companies and had not had any issues.

A Google search shows at least seven companies offering meth testing services for Rotorua properties.

Professionals McDowell Real Estate co-owner Steve Lovegrove said the biggest issue was the inconsistencies.

"Just recently we had a house with three different meth tests return with three different outcomes.

"Then we end up with these Mexican stand-offs where a home owner says their test came back negative but the buyer's test came back positive and we don't know which one is reliable."

Local property investor Debbie Van Den Broek said the industry was "quite deceptive".

"I've heard of cases where houses have come back with false positives, aimed at getting the more expensive test done.

"I know of two clients who received erroneous results, both from the same company," she said.

"I think even the most well-known companies are not necessarily as reputable as they make out to be. Property owners just need to be really careful."

Ms Van Den Broek said she found reputable companies by checking the background and credibility of those who owned them.

Graham Yorke, director of established region-wide testing company Meth Detection, estimated there could be dozens of operators with little or no knowledge or experience.

''All of my company field testers are licensed investigators under the Department of Justice ... and have been trained in forensic testing by a highly qualified training organisation,'' he said.

''In my view there should be standard practice involvement and minimum training levels set.''

His company had found the number of Bay of Plenty homes with moderate to high contamination levels had dropped. One in seven houses were detected a year ago compared to one in 12 now.

Consumer NZ chief executive Sue Chetwin said the organisation had heard complaints ''about what is happening in this space and support the development of a standard''.

''It does appear to be a cowboy industry. The testers are the same people who do the clean-up so it's in their interests to find meth.'

''Not saying that they are all like that but a cowboy industry has developed around people's fears.''

Insurance Council chief executive Tim Grafton said there were conflicting messages about meth contamination.

''Insurers are facing increasing numbers of claims from property owners who are faced with levels of contamination from tenants passively smoking P right through to contamination from meth labs on the property.''

The new standard would mainly cover sampling, testing and fixing contaminated properties, he said.

''And the requirement for all parties involved in the process to be trained or qualified to a high standard.''

Building and Construction Minister Nick Smith said the lack of a New Zealand Standard for meth testing and decontamination had led to differing views on how much properties were contaminated and how to fix them.

The new standard would address this, he said.

- Additional reporting Carmen Hall
What's changing

The new standard aims to provide guidance on methods, procedures and other supporting material that will ensure a consistent approach to managing the testing and decontamination of properties and contents. A committee of experts the Standards Approval Board approved had developed the standard.