Workers at Yorkshire Bank and HSBC branches contacted police after spotting victims shaking with fear as they tried to withdraw cash.
Danny Connors was locked up for eight months after a court how he intimidated two men, aged 83 and 91, into parting with cash.
A judge who jailed Connors said: “You preyed on two vulnerable aged men.
“In blunt terms you tried to work a con on people who were entitled to live peacefully. This was just naked dishonest greed and you interrupted their lives to get money for yourself.
“It failed because of the alertness, consideration and kindness of bank staff.”
Leeds Crown Court heard three men went to the 83-year-old victim’s home in Armley on June 11 this year and he agreed to pay them Â£80 to have his gutters cleared.
One of the men then told the victim he needed repairs doing to his roof.
Connors knocked on his door at 8am the next day and identified himself as ‘The Boss’.
Heather Gilmore, prosecuting, said three men were already on the roof.
Connors told the pensioner that he wanted Â£3,000 for the work.
He took Â£270 in cash and told the victim he would have to go the bank to get the rest of the money while he waited outside his home.
Miss Gilmore said: “He told him to say he was giving it to his family as bank staff were ‘bound to ask.’”
The victim went to the Yorkshire Bank branch in Bramley where staff saw him shaking so much he was unable to sign forms.
They called police when the victim told them what had happened.
Connors and the other men had left by the time officers arrived at the house.
Connors struck again at the home of the 91-year-old victim’s home in Swinnow the next day.
The prosecutor said Connors had been to the victim’s home earlier that month and had agreed a price of Â£100 for his gutters clearing.
He told the man he had done some work on his roof and he owed him Â£1,800.
Connors told the pensioner to go to the bank after agreeing to be paid Â£1,300.
Police were alerted by staff at the HSBC branch in Pudsey when the man explained what had happened.
Connors was arrested on June 20 and refused to comment when interviewed.
A surveyor inspected the roofing work Connors had done at both properties.
Miss Gilmore said a “weak slurry of cement” had been brushed on roof tiles and it was already beginning to crack.
The inspector described the work as of “low quality and of limited use or value”.
If the work had been done properly the expected cost would be around Â£350.
Connors, of Lands End Caravan Site, Doncaster, pleaded guilty to two offences of fraud. He has previous convictions for deception.
Robert Sandford, mitigating, said father-of-nine Connors had not been in trouble since 1998 and had admitted the offences at an early stage.
Mr Sandford Connors had been diagnosed as suffering from stress and anxiety and was financially dependent on his family.
After the case, an HSBC spokesman praised the efforts of bank worker Peter Bailey in helping the victim.
He said: “Protecting our customers from financial crime is an absolute priority for us, especially those who are potentially vulnerable. We are extremely proud of Pete and pleased to see that his vigilance has led to this rogue trader being brought to justice.”
Detective Inspector Richard Holmes, of Leeds District CID, said: “Connors preyed on vulnerable elderly victims and tried to trick them into handing over large sums for work he claimed to have done at their homes.
“The victims were directed to their banks to withdraw money but luckily staff became suspicious on both occasions and contacted the police.
“Criminals, like Connors, who seek to exploit vulnerable victims in this way are utterly despicable, and we hope the victims and the wider community can take some reassurance from knowing he has now been sent to prison.
“This case clearly illustrates why people should always be suspicious of anyone who calls at their home unannounced offering to do work. If in doubt, don’t let them in and call the police. We would also urge anyone with elderly neighbours to keep an eye out for them and challenge anyone you see calling on them if you’re suspicious.”
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