DOORSTEP criminals have conned an Alzheimer's sufferer for the third time.
She was a victim of gangs believed to sell information to each other about vulnerable targets.
Now, the 80-year-old woman's son is urging other people to be on the alert for the con artists.
Anthony Dale's warning coincides with a campaign against doorstep crime by groups including Kirklees Council's social services and the Kirklees Victim Support charity.
Mr Dale said he did not want his mother's name or home address in Kirklees revealed.
He said: "Doorstep criminals are cruel. They prey on vulnerable people and con them out of money.
"Possessions can be replaced. It's the emotional and psychological damage, and abuse of trust, that angers me."
In the latest incident Mr Dale's mother handed over £50 - all the cash she had - to a man claiming to have completed roof repairs.
Mr Dale, 50, a designer, said: "The home care assistant noticed a note my mum had scribbled which said `pay roofers £400' and became suspicious.
"She immediately contacted Kirklees Social Services home care team and Trading Standards.
"They did a return visit to try to catch the men, expecting they'd come back for the £350 my mum failed to give them. But they didn't show."
A year ago Mr Dale's mother gave £150 to men who claimed to have cleaned her gutter.
And five years ago a doorstep trickster, asking for some antiques, distracted her and stole jewellery worth £500.
Mr Dale said: "They get away with it because they're manipulative and the people they pick on, such as my mother, are confused.
"They also play on the fear factor, for example, saying things like `if you don't get these tiles done your roof might collapse and water will leak into your bedroom'.
"These people are very convincing. They don't want to work. They'd rather make their money from easy targets."
There are 150 reported doorstep crimes in Kirklees every year, but many more go unreported.
The latest campaign is encouraging more people to report such crimes.
Clr Andrew Marchington, chairman of Kirklees Safer Communities Partnership, said: "We want residents to feel safe in their homes and to reduce doorstep crime across the district.
"That's why we've launched a campaign which encourages more people to show cold callers the door and to report any suspicious doorstep behaviour."
Four hundred home care assistants from Kirklees Social Services have attended awareness-raising sessions run by West Yorkshire Trading Standards.
Paul Smith, principal officer at West Yorkshire Trading Standards, said: "Doorstep crime is particularly cruel, because perpetrators gain people's trust before ripping them off.
"It is a major blow to victims' confidence and their bank balance.
"And once you've been a victim you're more likely to be targeted again."