A regular commentator on Pattaya Rag has advised me that he arrived with 2 friends at BKK around 9.00am and went upstairs for a taxi. A price to Pattaya was agreed but then taxi only went about 3 miles from the airport before the driver swerved off the highway and drove in to a back lot. He said 3 Thai men demanded full payment even though they'd only gone 3 miles. My friend and his pals refused to pay and the Thai guys eventually backed down. He's not sure what would have happened to a tourist travelling solo.
I guess the only way to avoid this is to pay Bt3,000 for an official limo. Or at least take a photo of the car number plates with your smart phone and e-mail them to a friend for insurance. Make sure the driver sees you taking the photo. Might not help you but at least they'll find the driver!!!!!!!