"Money-motivated" cold callers pressurised elderly people into buying boilers that never arrived - and mocked them as they waited on the line.
CCTV shows the gang offer "free" boilers under a "government scheme" with an up-front fee of £299 or £399.
Only three out of 1,200 elderly victims received boilers - and all paid for them with 12-year credit agreements.
The company's three directors and a compliance manager are awaiting sentence for conspiracy to defraud.
They were caught on CCTV mocking people in footage seized by trading standards in Swansea - and will be sentenced on 15 April.
The images also showed those working at REC Home Audits using pressure-selling tactics in a culture obsessed by money.
Kyle Lewis, Darren Palmer and David Alford, along with Jason Cunliff were all found guilty of conspiracy to defraud after a trial at Swansea Crown Court, which followed a four-year investigation.
The CCTV from 2014 and seen by BBC Wales programme X-Ray, showed a manager shouting at his team: "What motivates you?" The team reply: "Money".
The company made up to £50,000 a week while it was operating in 2014 - and trading standards said the gang spent up to £5,000 on Saturday nights out in bars on Swansea's Wind Street.
The gang called themselves The Wolves of Wind Street after the Hollywood blockbuster Wolf of Wall Street, a film about corruption and fraud among stockbrockers.
One of the company's victims, Sonja Owen from Rhymney, Caerphilly county, paid £299 and only got a survey of her house.
She said: "I hope that they get sentenced and their assets taken off them, and they should be made to pay everybody back.
"Not only us, but everybody they've scammed."
The seized footage showed one telephone operator pretending to consult with a manager over a special offer while he was vaping and boasting to a colleague about the scam he was operating.
Rhys Harries, from Swansea Trading Standard,s told the programme: "They were using all sorts of techniques to try and manipulate people in to taking it out. They would pressurise people constantly.
"They would put pressure and pressure and pressure."
X-Ray, BBC One Wales at 19:30 GMT on Monday 25 March, and later on BBC iPlayer.