Not really 'worst'...
I had two friends, lets call them Sheila and Sharon, they were a couple, they ran a market stall for years and my Mother had known them through her work. I met them after my mother died, but she'd talked about them often, they talked to me about her... I mention this to make it clear, I met these people in person at least three times.
We continued to talk online, we ran a FB group together, they took in a friend, lets call her Kate, so now three women in their late 60's/early 70's are sharing a home. Sheila was police before she ran a market stall (joining her partner Sharon on the stall when she retired)... Kate ran another stall which is how they knew one another, I met Kate way back... when I met S & S..
For 5 years, I ran a FB group with these people, they visited my rental property local to them when I sold it, to clear it out and check everything was ok.
They were there for me when I had to go to hospital very poorly, they checked in on me when I was struggling, they were supportive and super kind, knowledgeable, funny...
Then Sheila died... and Kate became sporadic in contact, as Sharon struggled... then Kate went away to visit family in ireland...
Then Sharon died.
Kate didn't exist. Kate had never existed asides from them using the name of a person they'd known from the markets. They had fabricated this person living with them for YEARS, not just to me, to HUNDREDS of people.
There was no 'scam' apart from this invention of a person, they didn't create her to rip people off, they didn't do anything malicious or ill intentioned.
I'd love to know why they invented Kate, she was funny and kind ... but not out of the ordinary at all.
We found out from Sharons brother, and their neighbours.
It's really weird, but we all grieved for this person we'd believed in, rather than being angry we'd been lied to, it seemed better to grieve as if Kate had died like Sharon and Sheila.