UK's Serious Fraud Office seven-year-long operation found Australian Jeffrey Revell-Reade guilty of conspiracy to defraud due to a $126.4 million boiler-room fraud. The case is now being dubbed as the biggest ever scam of its kind in Madrid.

Revell-Reade, along with 8 others, were able to rob money from 1,000 unknowing investors from 2003 to 2007. All money amassed was used by the fraudsters to finance their lavish lifestyle or buy private jets, luxury yachts, overseas properties and sophisticated wine collections.

''The victims were deliberately charmed, lied to and bullied, whatever it took to make them send their money to these criminals. Over 1000 UK investors were defrauded by these criminals, who caused substantial financial damage and hardship," Serious Fraud Office's director David Green told the Telegraph London.

Authorities from New Zealand, Hong Kong and the U.S. worked with the UK agency under an operation with code-name Operation Steamroller.

Investigations dating back to 2012 showed that Revell-Reade was the grand mastermind of the scam. He was extradited from Australia in the same year.

Out of the nine defendants, including Revell-Reade, six were sentenced to serve three to seven years in jail. One 62-year-old defendant received suspended sentence. They were convicted in Southwark Crown Court in London on Wednesday.

"Boiler room" scams involve illegal brokerages making transactions over phone or via internet. Perpetrators will persuade victims to invest with promises of overwhelming return of investment, as explained by Mark Rantall, chief executive of the Financial Planning Association of Australia.

"There are often get-rich-quick schemes and unfortunately they target those members of the public that are vulnerable. Consumers need to be wary. If it sounds too good to be true, it more than likely is," Rantall told SmartCompany.

Rantall advised for investors to do background checks before placing their money or before heeding advice from brokers.

"They should also be wary of buying these sorts of products worth a substantial amount over the phone. You want to have a face to face meeting [for that]. Your hard-earned money is too hard to come by to just give it away," Rantall said.