Gerald Corrigan, 74, and his partner Marie Bailey, 67, are alleged to have been conned out of more than £200,000 before Mr Corrigan was fatally shot outside their home in a remote part of Anglesey, North Wales, in April 2019.
Richard Wyn Lewis, 50, denies 11 counts of fraud against a number of victims, including four involving the couple, and one count of intending to pervert the course of justice.
His trial at Mold Crown Court, which began on Monday, has heard the fraud charges are not linked to Mr Corrigan's murder, but came to light when police investigated his death.
On Tuesday, the jury was shown video interviews Ms Bailey had given to officers.
She said after Mr Corrigan was shot she had initially gone to stay with Lewis, who they knew as Wyn, and his partner Siwan Maclean, 52, who denies a count of entering into a money laundering arrangement.
Ms Bailey told officers Lewis, of Llanfair-yn-Neubwll, Holyhead, promised to "look after" her if anything happened to Mr Corrigan, who died in hospital some weeks after the shooting.
She said: "Wyn was saying things like: 'I'll buy a nice place for you'.
"I did not believe him. He was lying to me. He was not going to do anything like that, he was trying to manipulate me and he was trying to stop me from telling you what I really think."
Ms Bailey said Lewis told her not to tell police she had transferred £50,000 into Maclean's account, which she believed was to purchase a former school that could be sold on to a developer.
She said: "I couldn't stand up to him because he frightened me."
Asked what it was that frightened her, she said: "I think it was just the way he smiled, somehow there was a look about him and I knew there was something that wasn't right."
She said Lewis "isolated" her partner and took cash payments from them which they believed were related to the development and sale of their home, Gof Du, as well as to buy horses.
Payments, made in cash and handed over in a car park, included money for planning applications to allow their property to be developed into a campsite and sold to a buyer, John Halsall.
She said: "I have got this horrible suspicion that none of this happened and the money was just taken.
"I had been, over the last 18 months, saying to Gerry: 'Don't give Wyn more money, they're taking us for a ride, it's not true, they don't mean it, they're just taking our money.'
"Gerry said: 'No, no that's not true.'"
She added: "I believe Wyn was a confidence trickster and he has just taken Gerry's money.
"I believe this is a story and it is just not true because neither of us ever saw any paperwork."
She said Mr Corrigan knew "something was wrong" but hoped the sale of the property would go through and they could move on.
Ms Bailey added: "He said to me that when this is finished, this sale of Gof Du, we won't have anything more to do with Wyn because he is a liar."
The trial is expected to last up to six weeks.