At the hospital, they are both concierge and confidante. They explain procedures to patients and translate if they don't speak the language of the doctor.

Such is the life of a 'referral agent' here - which was what Mr Wang Chin Seng was said to be.

He was named in court documents on Friday as the person who found a kidney seller for CK Tang's executive chairman Tang Wee Sung, and who coached the potential organ sellers on what to say when they appeared before the hospital's Transplant Ethics Committee.

The committee has to be satisfied that the organ donor and recipient are related or have emotional ties before a live kidney transplant is approved.

But this is far from the usual duties of a normal referral agent, who acts more as a medical concierge, said those in the medical industry here.

'Patients see them as a hassle-free way to settle their treatment. These people are already sick, so they just want peace of mind when they come for treatment,' said a former health administrator at a private hospital.

The term 'referral agent' is not a definitive one. Some operate like travel agents, handling mainly hotel and airline bookings and basic referrals to hospitals here. But most seem to run independent outfits and offer more personalised service.

'It's not like you flip open the Yellow Pages in Indonesia and look for 'referral agents',' said one psychiatrist in private practice. 'Most of these people have no offices. They get business through word of mouth from satisfied clients.'

Their core business is to help patients source for the right medical services overseas - which includes medical tourism hubs like Singapore, Thailand and India - using their network of contacts.

They are usually citizens of countries where patients come from, such as Indonesia. Doctors noted that agents can be male or female, usually in their 40s or 50s. No one seems certain on how many of them are in the business, or how much money they make from these foreign patients. But one doctor pointed out that their pay 'should be not bad', since their clients are rich enough to seek medical treatment overseas.

However, not every doctor works with them. Of the 15 doctors and health administrators that The Sunday Times spoke to, five said they did not even know what 'referral agents' were.

Even those who have met them say they do not interact much with referral agents, other than to treat the patients they have taken to their clinics.

But there is a dark side to some of these agents. At least two doctors have had offers from agents to get them business if the former paid a commission.

One ear, nose and throat specialist said that three well-dressed agents have approached him in the last two years, offering to introduce foreign patients to him if he would give them a 10 to 20 per cent commission. He declined and they 'respected the decision'. 'I believe they target young doctors, who may be hungrier for patients,' he said.

All the doctors added that they do not personally know any doctors who offered commissions to these agents in exchange for getting them patients.

As for the elusive Mr Wang Chin Seng, no one seemed able to put a face to his name, although a couple of doctors said his name sounded familiar.

Do you know of referral agents and what they do? Send your comments to suntimes@sph.com.sg