After dropping out of school at 15, the Melbourne man got a job at McDonalds, moved out of the family home, and from there started working to support himself.
Only a decade later and his life couldn't be more different.
Just last month, Karagiozis says he sold his Lamborghini for "a respectful amount" of bitcoin — he won't say how much because "it's maybe not safe to reveal that".
He used to park it next to the BMW and Mercedes at his sprawling Templestowe property, up the drive along the manicured lawn, and just around the corner from the swimming pool and tennis court.
The property investor and self-described "serial entrepreneur" says he wouldn't be the success he is today if he hadn't taken risks, and now he's gearing up to take his greatest risk yet.
Like plenty of Australians and keen investors around the world, the 26-year-old has jumped onto the crypto-currency bitcoin, only he's looking to take his investment a lot further.
At an estimated cost of about A$15 million ($16.4m), he claims, Karagiozis plans to roll out the first ever nationwide network of bitcoin ATMs.
With his company Auscoin, he's planning to install 1200 of the machines across Australia and 300 throughout Asia to "help the average Joe get involved in bitcoin".
Karagiozis says he became involved in bitcoin back in 2012 when the price was "about two bucks". Now the currency he's been trading ever since is worth just shy of A$25,000 ($27,355).
He says he doesn't have a fairytale story like those guys you hear about "who just got lucky from investing a grand or so in bitcoin". His approach has been more methodical and he's built a business around it.
But he admits the currency has gone some way to help him get rich, and that's something he wants to share with the masses.
"The ATM is the easiest way for you to convert your cash into bitcoin," he says. "I know it sounds strange. I definitely agree that down the track cash will be obsolete but we're looking at a minimum of 10 years. Until then people need to pay for their food etc with cash."
Thought it seems counterintuitive to use old fashioned cash machines for an online-only encrypted currency system, but the way Karagiozis explains it, the ATMs will help people use their bitcoin wallets more like a high-interest savings account rather than hoarding the currency like gold.
Sam Karagiozis describes himself as a 'serial entrepreneur'. Photo / Supplied
"The idea is people tend to put their savings into bitcoin, and if they do need cash from for anything they just take it out. Nine times out of 10 the cash has appreciated," he says.
Basically, Karagiozis wants to see mass adoption of crypto-currency across Australia, and he wants to be the guy who brings it here.
He's already had his first bitcoin ATM up and running at his Thornbury Souvlaki store for nine weeks, and says in that time it's been used to transact "just under a million dollars".
The second ATM was launching on Monday night at Chadstone Chase shopping centre's new food court.
"They're going to go into every shopping centre in the country, and then we're looking at airports," he says. "I believe we're the first people in the world who have actually commenced a nationwide rollout."
Karagiozis considers among his greatest achievements something that happened just last week.
A camera crew keen to check out his Auscoin project visited Souvlaki GR, and each bought about $100 in bitcoin.
He says the mature cameraman — who entered the takeaway store with no understanding of crypto-currency, and wouldn't have a clue how to set up an account or conquer the risk of scams that can come with buying currency online — not only bought some bitcoin there and then, but returned to the store later in the week to buy up again.
"I've just taught someone who's 65 and doesn't know anything about the blockchain to use bitcoin," he says. "That's what it's all about."
Along with the ATM network Karagiozis plans to ride off the back of bitcoin's success and launch a new type of crypto-currency that he believes is perfect for mass-adoption in Australia.
"Our vision is for Auscoin to become Australia's payment of choice as bitcoin becomes a store of value (like gold)".
He says his bitcoin machine is already getting a workout in his Thornbury souvlaki store. Photo / Supplied
It seems like a lofty goal, but among those who share his confidence Sam counts Australian tennis bad boy Nick Kyrgios.
After weeks of meetings, Karagiozis says the sporting celebrity last week confirmed his affiliation with the brand and shared a video on Facebook voicing his support.
"Bitcoin has been the talk of the town. AUSCOIN is rolling out 1200 bitcoin ATM's across Australia," Kyrgios wrote, sharing a video shot inside the souvlaki store sharing an outline of the project with more than 366,000 followers.
One follower commented: "That Kyrgios is servin' Auscoin up like an ACE, hangin' bitcoin in ya face, makin' mills of bills while his backhands sendin' thrills."
We can't say exactly what that means, but it sounds enthusiastic.
According to its website, Auscoin raised more than A$1m ($1.09m) in its first seed round which was open for just 24 hours.
Sam's isn't the only one in the crypto-currency ATM game. According to Coin ATM Radar there are 23 bitcoin ATMs/tellers in Australia. A project to convert 2900 existing ATMs and roll out 500 new ones with bitcoin processing capabilities was announced by another company in September.
But Mr Karagiozis believes his point of difference lies in Auscoin tokens — a currency he's confident will take off in Australia.
