These issues included price variations and the company's responsibility for delays and outstanding council invoices.
The BSA determined the complainants were portrayed unfairly and TVNZ has failed to take reasonable efforts to ensure the programme was accurate and did not mislead.
In a statement, the authority said Fair Go's presentation and discussion of issues was likely to have caused "unwarranted harm" to the complainants' reputation.
"We are conscious the Fair Go series, and its investigations into various consumer issues, is of public interest and carries high value.
"However, where a person or organisation referred to in a broadcast might be adversely affected, their comments must be fairly depicted."
The authority said in this case the broadcaster had not met its obligations.
A TVNZ spokesperson said the broadcaster accepted the BSA's decision.
TVNZ has been ordered to publish a statement summarising the authority's decision and to pay $2000 legal costs plus disbursements to the complainants and $1000 in costs to the Crown.