A soldier killed himself after paying £13,000 for training with a property company that promises to help people become "financially free".
The family of army reservist Danny Butcher, 37, said he never made the money he thought he would.
Dozens of people want refunds from Property Investors, which has been described as operating like a "cult".
The company, run by former illusionist Samuel Leeds, said: "People should only purchase courses they can afford."
Mr Butcher, from Doncaster, had spoken about his mental health in the past and his family said he had existing debt before he took on loans and credit card debt to pay Property Investors.
His family said he had been led to believe he would make enough money from property deals and rental income to replace a wage or salary.
Mr Butcher's widow Charlotte, 32, said: "I think that he felt that he'd let everyone down, that he'd messed everything up and that there was no way out of it.
"All he wanted was his own chance at making something of himself for me and his son, he saw this as his opportunity.
"Obviously taking out all of the loans, he put himself on the line, but it was a bit like 'yeah it's scary but without risk there's no reward'.
"He genuinely thought this was his chance because of how easy they made it all sound."
Property Investors puts on free two-day crash courses, offering people the option to sign up to a training academy where they will learn how to become "financially free" by investing in property.
The company described Mr Leeds as having "found his own success" after attending training courses, with his wealth coming "primarily from his property investment activity".
Mr Leeds posts videos on YouTube nearly every day promoting his methods. In one he joked that he would punch people in the throat unless they subscribed to his YouTube channel.
In one clip he promises to work one-on-one with his customers, to provide "a custom, tailored, bespoke plan" and "hold your hand, make it happen".
Mr Butcher attended a free course in March with his brother-in-law Glyn Jones.
Mr Jones said: "It felt like brainwashing, like a religious cult kind of thing but done on a much smaller scale.
"What he's offering never appears, I don't see how it can."
According to his wife, Mr Butcher's "gut instinct" told him not to sign up for the academy and he held out for two days before changing his mind, swayed by the promise of exclusive mentorship and one-to-one training.
Mr Butcher's family said he did not get the support he had been promised.
The company said academy members had access to weekly video calls and monthly webinars with specialist property coaches.
After failing to make any money, Danny Butcher took his own life in October.
At the time, Mr Leeds made a public statement on Facebook: "I am deeply saddened to hear that Danny Butcher took his own life.
"This tragic news comes as a great shock to many and I am heartbroken that this has happened. My thoughts and prayers are with Danny's family at this time."
The BBC has become aware of dozens of people who have said they signed up for Property Investors' training and now wanted their money back.
At least 78 people are trying to claim back more than £200,000 between them.
Dianne Granville got a refund from Property Investors in 2018 and has been helping a group of people to try to get their money back.
She said: "There are very vulnerable people out there and he's preying on them.
"I'm lucky. I realised what was happening to me and I dealt with it."
In a statement, the company said it was "proud to run the largest property investment training business in the UK".
"We are humbled to have the opportunity to help thousands of people on their journey towards financial freedom through property investments every year," the statement said.
Army veteran Andrew Whyte, who served in the Falklands and Afghanistan, said he intended to pursue the company through the small claims court.
He said he handed over his armed forces pension payout to cover the cost of the training.
Mr Whyte said: "I ended up having to skip meals or have Pot Noodle sandwiches, stuff like that, the cheapest tins and cheapest noodles, just to have food and to eat.
"If I was living on my own I'd probably be on the streets by now. I'd be surviving off the street if I hadn't had the support from friends and family members."
In a statement, the company said: "While we are not lenders or financial advisors, our stated view is that people should only purchase courses that they can afford."
It said there was no obligation for people who attended the crash course to sign up for further paid training, while there was a two-stage application process for the training academy and a 14-day cooling-off period during which people could request a refund.
The company said any requests for refunds outside the cooling-off period would be considered on a case by case basis but it was not "fair or right" for people to attend courses and then "seek not to pay for them with no legitimate reason".
A BBC reporter went undercover on one of Property Investors' crash courses and filmed a speaker telling people it was possible to make up to £50,000 a month from something called "deal sourcing".
This involved finding houses for sale on property websites such as Rightmove and working out how much rental income they could generate before selling this information to investors.
On the first day of the course, which lasted from 09:00 to 23:00, the reporter was invited to apply for the training academy.
During a selection interview the next day, she was encouraged to sign up despite saying she was unable to afford it and would have to increase her credit card limit to cover the costs.
Property expert Bruce Collinson said: "There's nothing easy about property investing, you get out of it what you put in to it.
"This is a scheme, an investment, a gamble, where you could lose the lot and if you haven't got anything to start with then where are you going to end up? Bankrupt, repossessed, if you have property, or worse."
In a statement, the company said: "Investing in property is not for everyone. We do not advise those who cannot fully commit to the time and effort it takes to participate."
There is currently no regulation of the property training industry in the UK, anyone can set themselves up as a trainer and no-one verifies whether they are what they say they are, or if they provide the training they promise.
This is something Mr Butcher's family said they wanted to see changed.
His father Alan said: "The only thing I can do for Danny is to try and make people aware so they don't end up wasting their money and putting themselves in a bad place. If it does that, what's a meaningless loss of life won't be quite so meaningless."
In a statement, the company said: "We think that debate about standards and regulation in our sector is a good thing and it is something that we look forward to actively leading as it develops."
If you or someone you know has been affected by the issues raised in this story, help and support is available at bbc.co.uk/actionline
Inside Out (Yorkshire and Lincolnshire) investigates the company charging thousands for training courses on BBC One at 19:30 GMT on Monday 20 January and can be seen afterwards on BBC iPlayer.