Consumer New Zealand has given a warning over Auckland-based GET Design and Sales, which it says has left customers thousands of dollars out of pocket.
GET Design and Sales sells its products through the websites kiwi-built.co.nz, myDIY.co.nz, and econobach.co.nz.
Several customers have complained they are owed money, including Palmerston North resident Steve Wrathell, who wanted to build a sleep-out.
He said he paid GET Design and Sales almost $12,000 in October last year, and was promised the new build by the start of January, but three months on has received nothing.
"I've had to act on the assumption that my money's gone and that nothing's coming, so I've had to start from scratch," he said.
New Plymouth man Scott Walls said in his case problems started over a year ago when materials he had paid for never arrived on site.
"I started, I guess, doubting some of the explanations I was given, so I started making my own inquiries and found down the line that what they were telling me wasn't quite correct and I ended up canceling the contract with them part way through the build," he said.
Mr Walls said the company owed him almost $15,000 and had repaid $2000.
He had since initiated legal action against them, and hoped it would resolve a few of the issues.
" certainly want to try and get my money back that I've given them and they haven't delivered on, but then also trying what ever I can do legally to ensure that they don't continue to do this to other people."
Consumer New Zealand chief executive Sue Chetwin said it issued the warning following several complaints that money had not been paid back.
"We have spoken to one of the principals [of the company] and they admit they've got troubles, and they say they were going to pay some people back by the end of February, but that didn't happen.
"So we're really concerned that the websites are still operating and that people may be, I guess, misled into giving money to these DIY constructions and that they might be left out of pocket."
Ms Chetwin said Consumer New Zealand will be filing complaints with the Companies Office and the Commerce Commission.
GET Design and Sales has not responded to calls from RNZ for comment.