Monsignor Henry Docherty – a friend of Pope Benedict XVI – was approached by Allan McAllister and three other men while standing in his driveway.
They pretended they knew him through church circles and persuaded him he needed work done on his drains and roof.
But Mgr Docherty grew suspicious and called the police.
He handed them photos and papers which helped detectives track the men down.
They discovered that there nothing wrong with his drains and he had been charged almost three times the going rate for the job.
McAllister was originally accused along with Peter McAllister, 29, Paul McKillop, 47, and Ryan Johnstone, 37, of obtaining £17,180 by fraud.
But last week, 29-year-old McAllister admitted gaining £2000 cash and a £8000 cheque by fraud at Mgr Docherty’s Glasgow home between July and August 2010.
A plea deal saw the amount reduced and let the other three men walk free.
Last night, a friend said: “Mgr Docherty is an intelligent man and his quick thinking definitely helped get McAllister caught. This man built up a trusting relationship with Mgr Docherty before introducing more work that supposedly needed done. When he discovered that he had been overcharged by a substantial amount and lied to about what needed done, he felt dreadful. He managed to stop a cheque for £8000 but he had already paid him in cash for other things. That money was savings he had accumlated over the years. He just hopes his actions have stopped McAllister and the others doing the same to other people.”
Mgr Docherty paid the gang more than £4000 after McAllister told him they had found a sewage problem in his drains.
The conman pretended to speak to Scottish Water on Mgr Docherty’s behalf to sort out insurance.
He even told him he would do the work for half price, charging £10,000 for a job he claimed usually cost £20,000.
But suspicious Mgr Docherty called Scottish Water himself to check and McAllister’s web of deceit began to unravel.
The priest discovered that no call was ever placed on his behalf, that no work was required and that he had been overcharged.
Mgr Docherty managed to block the cheque but lost the cash.
And he is not the only elderly client McAllister has tried to con.
In 2010, we told how McAllister and his dad Peter ran AM to PM Roofing and took at least £80,000 for shoddy and incomplete jobs or work that was not necessary.
Trading Standards took action and said the con was “one of the worse cases of doorstep crime our officers have investigated”.
McAllister will be sentenced for the latest fraud next month.