Age Concern co-ordinator Wayne Stringer said the elderly victim was at the point where "she hasn't got anything left''.
The advocacy group was informed by a local supermarket on Tuesday the woman was being mistreated by two people in their early 20s.
Mr Stringer said initially the young woman showed up at the pensioner's Oamaru address with a baby and said the infant needed food and nappies.
"This lovely lady, who's only in her 80s, gave her some money.''
The young woman soon approached the pensioner again, this time with the story that she was pregnant and needed to go to Dunedin for a scan. She begged for money to get to Dunedin.
"The next trick was she said she had breast cancer and needed to go to Dunedin again.
"In the end they were taking the old lady to the supermarket for groceries and she was paying for them.
"It was the supermarket that let us know something wasn't right and now we've come to the point where she hasn't got anything left.''
Mr Stringer said incidents like this were not rare.
"This goes on all the time.''
He said police and the pensioner's family were informed of what occurred and were now involved.
"We're working very closely with the police.''
Mr Stringer said that the worrying aspect of the elder abuse case was that it was unknown if the pensioner was the only elderly person the two young people had targeted with their stories.
"If they're showing up on her doorstep, who's to say they're not showing up elsewhere. The really good thing about it is the supermarket has told us and now we know it's happening.''
He said the name and address of one of the young people involved was passed on to police.
He said it was a case of manipulation of a person of sound mind.
"She's just a very kind lady and once they've started they've just kept going.''
Mr Stringer appealed to the public to come forward if they were also targets of the couple or if they suspected other people were the target of elder abuse.
Yesterday was the official World Elder Abuse Awareness Day.
● To contact Age Concern's national office call (04) 801-9338 or call Age Concern Waitaki on (03) 434-7008.
