Two brothers from that group approached an Auckland man of 79, offering to clean his roof. They later insisted more work was needed, eventually taking almost $20,000.
Today's love rat scammers usually targeted women in wealthy neighbourhoods, Hartley Moore said.
She said concerned relatives would approach private investigators.
"All of a sudden their mother's withdrawn. She doesn't seem to need them to take her out."
Sometimes concerned family members had their motives questioned, with insinuations about inheritance money.
But Hartley Moore said her clients would tell her: "My aunt can leave it to the SPCA, the Cancer Foundation, but I don't want my aunt to give it to this guy."
"I met a client who met the guy at a car wash. They like the same things. She ended up giving him $900,000, and she was one of many," Hartley Moore added.
"This guy was in his 70s and she was in her 60s but usually it's an older woman and a man about 20 years her junior."
The scammers led double lives, and Hartley Moore said many of them had sexual affairs with the older women.
"The guys are married, with families, and they're taking home the spoils of their work to their own family."
She said a scammer's wife might believe her husband was altruistically helping the elderly woman.
Hartley Moore said the charlatans sometimes devised glamorous or exotic-sounding back stories.
"Like any abusive relationship, they will start isolating the older person, isolating the victim, maybe going into the bank with the victim."
She said the United States had strengthened legal protections against elder abuse.
America's Elder Abuse and Prevention Act established elder justice coordinators nationwide and mandated improved data collection about elder abuse.
Groot said lawmakers here could consider tougher penalties, or contemplate whether a victim's age should be deemed an aggravating factor in fraud offences.
FOR HELP: If you suspect elder abuse, regardless of whether there is identifiable criminality, call 0800 32 668 65 for free (0800 EA NOT OK) for advice and support for the older person. You can also text 5032 or email support@elderabuse.nz
If you're concerned about anybody's immediate safety, call 111