The Earthquake Commission says some unscrupulous tradesmen are persuading homeowners to get drain and sewer repairs done without prior authorisation, putting householders at risk of losing money.
EQC general manager Bruce Emson says people need to contact the Commission and prove the damage is quake-related before work is done.
He says the commission has no business relationship with contractors doing earthquake repairs and no liability to meet the cost.
"Say they determine it's a $5000 repair and actually we assess it's a $1000 repair, the customer is exposed to that $4000, and that's where we're urging them not to commit to the contractor directly without authorisation from EQC."
Mr Emson says work can be paid for retrospectively, but the Commission is obliged to pay only what it thinks the job was worth, and that can leave people out of pocket.