It revealed a litany of problems that he said were probably present before the sale.
"People think they are going to save money but in the long term it could cost many more thousands to rectify anything," Mr Dedden said.
Mortgage Link broker Stuart Wills said his clients usually completed due diligence, but he had heard of people buying houses unseen.
He said buyers needed to take some responsibility themselves. "Realistically, they need to seek legal advice, seek advice on property and get a builder's report."
ASB Bank head of home lending Vince Clark said buying a home was a big commitment, so ensuring the property met expectations was important.
"It is therefore extremely important for customers to conduct proper due diligence by using the appropriate professional advisers to identify any issues before committing to a contract."