A ransom of £20,000 was demanded for Joseph Raca, from Northamptonshire, after he was taken in by the international fraud.
The 68-year-old was kidnapped at Johannesburg Airport a week ago after responding to a letter about a "business transaction," said the South African Police Service (SAPS).
Mr Raca was a victim of the so-called "419 Nigerian letter" scam which offers cash pay-outs in return for moving large amounts of money between countries.
Rather than getting rich, Mr Raca was kidnapped by a man and woman and his wife received a telephone call demanding the ransom.
He was only released on Wednesday near the airport, after his kidnappers got nervous, said detectives.
British police helped trace the kidnappers to the East Rand area of the city.
A SAPS spokesman said: "Intensified overt and covert police inquiries obviously made the kidnappers extremely nervous."
The three suspects were arrested as they were about to collect some ransom money at a bank in Johannesburg.
Detectives are still searching for other gang members.
Mobile phones and a fax have been seized.
British and South Africa police worked together on the operation.
An officer from the National Crime Squad and one from Northamptonshire Police flew to South Africa.
The National Criminal Intelligence Service said recent success in fighting the Nigerian fraud meant criminals were sending the letters from other countries such as South Africa.
The correspondence appears to be from an "official" foreign government or agency which offers to transfer millions of pounds into the person's personal bank account.
More than 78,000 "419" letters were received in London alone over three years, in a confidence trick which could be costing Britain up to £150m a year.