Builder Mike Harris was persuasive.

In March last year, he told Tony* and his wife that if they wanted their major renovation to get underway, they needed to pay $140,000 in costs outside their contract so he could quickly buy building supplies.

"He really, really led us to believe that it was critical to lock in prices for those materials and to lock in trades and timing, which was exciting for us at the time," Tony said.

Mr Harris assured them the job would be "done by the end of last year", Tony said.

But when the ABC visited the couple's Melbourne property last week, Tony was standing in a gutted house littered with construction debris and the back half ripped off — a skeleton of the planned two-storey rear extension jutting into the sky.

Tony said Mr Harris's company, MJ Harris g

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