More people complain about the telecommunication industry than any other sector, a report says.
The Commerce Commission report found there were 7270 complaints for the year to 30 June - a 31 percent increase in 18 months.
The vast majority of the complaints were made under the Fair Trading Act, and covered pricing practices, representations about goods and services, warranties and guarantees, and traders not delivering purchased goods.
The telecommunications industry was the biggest single category, with Vodafone receiving 186 complaints, followed by Spark, with 180 complaints.
Incorrect billing was one of the main problems.
Vodafone and Spark said they were very disappointed with the comments made in the commission's report.
In a statement, Vodafone said while one complaint was one too many, the Commission's report was a raw measure only and not all complaints indicated there was a problem.
The company said its own benchmarking indicated a 42 percent drop in consumer complaints made directly to Vodafone and a rise in customer satisfaction.
Spark made a similar comment, saying the 180 complaints received by the Commission were only complaints, and were not necessarily upheld by the Commission.
It also said 180 complaints was a tiny fraction of its more than 3,000,000 customers.
The commission itself acknowledged its publication was a measure of raw complaints only, but said it still had value as an indicator of public concern.
"Telecommunications continue to be the most complained about industry, with the number of complaints increasing by nearly a third on last year," Commissioner Anna Rawlings said.
"This trend reinforces our decision to make retail telecommunications a priority focus area for the coming year across both our consumer and regulation work."
After telecommunications, the next most complained about category was domestic appliance retailers.
Noel Leeming headed the list there, with 82 complaints, followed by Harvey Norman with 45 and PB Technologies with 32 complaints.
The charges included pricing practices, especially during advertised sales, which appeared to be misleading.
Some consumers complained about advertised goods being unavailable and instead used as bait to lure customers into a store.
Motor traders were the third biggest subject of complaints, with a quarter of them relating to the real condition of vehicles for sale.
The next big areas were electricity retailing, groceries and and supermarkets.
As well as breaking down economic sectors, the report looked at the way people shopped.
"With the continued growth of online shopping, we are now seeing more than 40 percent percent of Fair Trading Act complaints relate to consumer experiences online," Ms Rawlings said.
"While internet shopping is convenient and gives consumers access to new products, consumers need to research the traders they intend to buy from.
"They need to pay attention to additional costs such as booking fees, the currency they are paying in, and fine print disclosures."
Top 10 traders who generated Fair Trading Act complaints:
- Vodafone New Zealand
- Spark NZ
- Foodstuffs NZ
- 2degrees Mobile
- Noel Leeming Group
- Air New Zealand
- Vocus Communications
- Progressive Enterprises
- Wilson Parking