It takes a crook to deal with a crook, says Mr Wong Kee Soon.

This is why the 63-year-old believes he has a special advantage in his chosen profession of helping borrowers with loan-shark woes.

After all, he used to be a loan shark and was one of the leaders of a secret society.

"I was a loan shark, so I know their scare tactics and I'm not afraid of them and will use (the same tactics) back on them. If they shout at me, I will shout back. I also tell those under my care not to be scared," he said.

And it is perhaps because of his past that he insisted on wearing his spectacles for the photo shoot when speaking to The Straits Times at his home last week.

"My wife says I look more approachable like this. If not, I look very fierce, maybe even fiercer than a loan shark," he joked.

Growing up in a coffee shop in Geylang, the founder of Adullam Life Counselling was influenced by the "colourful characters" who patronised his father's shop.

Adullam is a voluntary welfare organisation that helps individuals and families with debt problems or who owe money to licensed or unlicensed moneylenders. It was established in 2013.

"(Geylang) was the centre of you-know-what. There were more bad people than good people at the coffee shop. And I started hanging out with them," said Mr Wong.

He recalled how some patrons would have bags of money with them, intending to visit illegal gambling dens in the back alleys. He also remembered pimps who came for coffee after parking their fancy cars.

It was against this backdrop that Mr Wong started gambling at age 14. By 16, he had joined one of Singapore's biggest gangs with ties in Malaysia and which had more than 10,000 members.

"A loan shark took me under his wing, and I would tag along when he went to collect debts," he said.

After completing his O levels, with A1s in English and Chinese but dismal grades for other subjects, he started working full time at the family coffee shop and bakery.

In the day, he would work hard, helping out at the shop. But at night, after a change of clothes, he would harass borrowers or take part in gang clashes.

"My parents had eight children and worked long hours, so it was impossible (for them) to keep track of all of us," he said.

To get rid of any hint of his night out, he would take a shower at the bakery and change back into his work attire to make it look like he had been working all night.

He said one of the tactics the gang employed was having members approach borrowers with shouts and threats to burn down their homes, but the leader would remain calm throughout.

"The lao da ("big leader" in Mandarin) would then ask for payment softly, with a smile on his face. This was how they instilled fear. It was reverse psychology in a way."

Mr Wong applies similar tactics when dealing with loan sharks or gang members to negotiate the debts of borrowers who come to him for help at Adullam. He has no qualms about speaking to them over the phone or - his preferred method - in person.

"If I can meet them (the loan sharks), perhaps I can also help them turn over a new leaf," said Mr Wong, adding that he sometimes has to rely on his past connections with senior gang leaders.

He recounted an incident that happened after he left the gang in the late 1980s - he was asked to help a youth who wanted to leave a gang.

"I approached the gang and told them that he wanted to leave. They asked, 'Who are you to tell us this?'

"I gave them my name and calmly told them to relay it to their leader. The boy was allowed to leave without any fuss."

For 15 years, Mr Wong lived a "double life" and managed to keep his gang involvement hidden from his wife, whom he married in 1980.

He even made friends with police officers in his neighbourhood and gave them tip-offs about the activities of rival gangs.

"Being part of the gang made me feel powerful. I felt like a king because I was respected among members. But I was very careful to keep it a secret," he said.

Even after opening his own restaurant and catering service, Mr Wong continued his underworld activities.

"I wouldn't go out so often any more because I had a family. But I was considered one of the masterminds in the secret society, so my role involved advising members on matters like capturing more gang territory," he said.

His life-changing moment came soon after doctors told him he had to undergo an operation as the cartilage in his knee caps had worn out.

The pain had been plaguing him for many years before that, and one day, out of boredom, Mr Wong, then 31, decided to pick up a Bible that was tucked away in a corner of his home library.

"I was overwhelmed by a sense of desperation and called out to the Christian God for help," he said.

It was only days later that he realised the pain had disappeared.

"That's when I became a Christian and decided to go from harassing others to helping those on the receiving end," he said.

It is his past as a gang member that has influenced the way he helps other people to settle their loan-shark woes today - tactics that are known to be a little "unconventional".

But he said loan sharks today have changed tactics.Most hide behind anonymous or overseas numbers and never take him up on his offer to meet and negotiate.

"They have changed tactics, so I have to change mine as well. For now, my advice (to borrowers) is to ignore them and cut off all contact, even if it means changing your contact number and lying low for a while," said Mr Wong.

"It's because of who I was in the past that I know how to handle these people, and I can turn around and help those harassed by loan sharks."