After Consumer told the clinics they had been involved in its investigation, two said staff would be trained as a result; one said "the whole industry needs to be trained better"; one declined to comment and three did not respond to emails or calls.
Consumer NZ chief executive Sue Chetwin said the risk of beauty clinics offering treatment was that staff might not recognise a skin lesion as a symptom of cancer.
"Given New Zealand's high skin cancer rate, we think beauty therapists should steer clear of this type of treatment and leave diagnosis to the doctors."
Consumer says the Auckland Council health and hygiene code of practice states that only health practitioners should remove skin lesions. Members of the NZ Association of Registered Beauty Therapists - of which membership is voluntary - are prohibited from removing unidentifiable lesions and skin tags without permission of a doctor. None of the seven Auckland clinics is a member.
One of the clinics identified by Consumer is run by a registered nurse, who told the Herald she specialised in removing skin tags, but if people were concerned about moles or other skin lesion she referred them to a doctor.
She said she would not have misdiagnosed a mole as a skin tag and she did not know who the mystery shopper was, so can't check her records.
Associate Professor Amanda Oakley, a dermatologist, said the nurse's approach to skin tags and moles was the right one.
She said a dermal melanocytic naevus is a harmless mole. The risk of asking beauty therapists was they might not be qualified to say it was a mole as opposed to a basal cell carcinoma or a melanoma.
"Is that person qualified to say, 'I know this is completely harmless'. You don't want to get it wrong.
"If they are unable to give a firm diagnosis or are thinking of destructive therapy the patient should be informed they need to go to a doctor, usually a GP, to have the lesion checked.
"Moles are removed in medical practice but they are sent to a pathology laboratory to make sure that's what they are and not any of the worrying things."
Dr Oakley said beauty therapists should confine themselves to "creams and things that don't damage the tissue" and leave potentially harmful treatments like laser to others more qualified.