When Suvarnabhumi airport was opened on Sept 28, 2006, illegal tour guides and taxi drivers moved from Don Mueang airport to the new airport.
They still frequent the passenger terminal and departure floor.
Illegal tour guides and taxi drivers are often in league with each other. Tour guides bring travellers from inside the passenger terminal and send them to taxi drivers outside the building.
The guides receive 100 baht to 500 baht per passenger from taxi drivers, who then charge fares that are five to 10 times higher than standard fares. Drivers also take travellers to guesthouses, hotels and shops where they receive commissions. They even drop en route passengers who try to bargain for lower fares.
Airports of Thailand Plc (AoT) started serious suppression on Aug 9, 2009. Punishment was intensified from a fine of up to 1,000 baht to 2,000 baht and one-year imprisonment as culprits are now also charged with trespassing. If wrongdoers coerce or threaten travellers, they will be liable to five years in jail and fines of up to 10,000 baht.
Serious suppression saw the mobilisation of police from Region 1 Provincial Police, tourism police, local police, land transport officials and AoT guards. They initially formed three teams of 39 officials who took turns to stand guard at Suvarnabhumi airport around the clock.
There were also rapid movement teams of AoT who arrested culprits swiftly. AoT installed more surveillance cameras to monitor crimes at the passenger terminal.
In the first four months of the suppression, more than 4,000 illegal tour guides and taxi drivers were arrested.
Despite the campaign, Suvarnabhumi airport director Somchai Sawasdipol admits the presence of illegal guides and taxi drivers continues at the six-year-old airport.
He said the wrongdoers mainly target foreigners.
Suppression brings down their number but the rip-off merchants manage to move from the arrival area on the second floor to departures on the fourth floor of the terminal, where some arriving passengers exit.
AoT plans to install one-way gates by the end of this year to block passengers from exiting on the fourth floor.
Kittipong Kittikachorn, acting director of AoT's special operations centre, said one-way gates were tentatively installed at Gate 5 on the fourth floor of the passenger terminal. When such doors are completely installed, there will be more legal and registered taxis on the first floor because more arriving passengers will wait for taxis there.
Since the suppression started, 16 people have been charged with trespassing. About 10 people are arrested daily for being illegal guides and taxi drivers at the airport.
Illegal taxi services at the airport are often run by organised operations backed by influential people. But there are also individuals who drive their own cars to the airport and pose as taxis.
They not only operate during the day - many prey on foreigners from 11pm to 2am when many flights arrive from Europe and only three security officials are on duty.
They even operate on the first floor where there are registered taxis. They stand among passengers when queues for legal taxis are lengthy and offer services in person. Some passengers follow them in the belief that they are registered taxi drivers.
Pol Lt Col Piti Trikalnont, deputy director of AoT's special operations centre, said authorities was first alerted to illegal guides and taxi drivers in 1989. That was when a honeymooning Japanese couple were lured by an illegal taxi driver at Don Mueang airport. They were robbed and attacked in Pathum Thani province. The husband was killed and his wife survived.
Mr Kittipong said the illicit business continues as an illegal taxi driver can make 2,000 baht to 3,000 baht a trip.
For example, they charge 1,300 baht to 1,500 baht for a ride from Suvarnabhumi airport to Pattaya where they also receive commissions from the hotels and shops they bring tourists to.