Complaints to the Commerce Commission have increased by more than 20 per cent in the year to June 30, with telecommunications and retail service providers top of the offending list.
The consumer watchdog says it received 8964 complaints in the 2018/19 year, with telecommunications and retail service providers receiving 727 complaints, followed by online ticket reselling (think Viagogo) with 585 complaints and then domestic appliance retailers.
Common themes of the complaints included consumers saying they were charged fees they were not told about, incorrect bills and contracts they did not agree to.
More than 8000 of the complaints received in the year were Fair Trading Act-related, and more than 300 relating to breaches each in the Commerce and Credit Contracts and Consumer Finance Acts.
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Motor vehicle retail and construction industries were among the top five industries that received complaints relating to the Fair Trading Act, receiving 449 and 365 complaints in the year.
The commission received 189 complaints about airlines, 162 about grocery products, 151 about supermarkets, 143 about vehicle rentals and 138 about electricity retail.
There were also 21 complaints about children's toys, eight about household cots and five about children's clothing.
Over the past five years, the Commerce Commission has recorded an 80 per cent increase in complaints related to online retail - these make up a third of all Fair Trading complaints.
Commerce Commission chair Anna Rawlings said increases in complaints related mostly to matters of Fair Trading and were up by more than 1500 in the year.
Rawlings said the online ticket reselling industry experienced a 63 per cent increase in complaints in the year.
"The increase in complaints about online ticket reselling is led by the unprecedented number of complaints about Swiss company Viagogo. We are taking High Court proceedings against Viagogo and can't comment further on that while the matter is before the 'courts," she said.
"We can only investigate what is causing the most harm to New Zealanders and complaints help us prioritise, but they also show us where consumers and businesses need more information to understand or comply with the law."
Rawlings said complaints to the commission informed policy making.