Airport "taxi-mafia": On arrival in the airport you will be met by a number of welldressed gentlemen or even alluringly dressed ladies who endorse this or that taxi service. Or they may politely ask Have you got reservation? as if this was a normal routine question. What they are really after is taking the tired and confused newly arrived tourist - you - to a hotel of their own choice, at a taxi fare that the driver decides. Just pass them by, decline with a smile, and do not engage in any discussion with them.

Instead you should go all the way through the halls of the airport, out the exit, and approach the official airport taxi service run by the police. Here you will pay a service charge of 50 baht - and get a Taxi Ticket whith the driver's name and a booking number, plus the name of your destination written in thai. On the back side of the ticket is a formula for complaints, ready to be mailed as a postcard to the Public Transportation Center. The formula speaks its own clear language about the most common taxi schemes aimed at foreigners: you can tick off printed complaints like Overcharged fare metered taxi - Switch off the meter - Drop off passengers before reaching destination.

After arrival, always flag a moving taxi, not one waiting by the hotel or tourist site, and check their rates before you accept it - you should only spend about B35 to start, with an average fare of less than B100.

Avoid "friendly" tuk-tuk drivers who may present themselves as guides and speak pretty good English. They hang out near major tourist sites, hotels and shopping areas and they'll tell you the temples are closed (holiday, cleaning, the King relatives passed away, whatever). Instead of the temples, they offer to take you on a cheap day-long tour of the city. But you may find yourself involved in their  "get rich quick" scheme: As you are on your "tour", you could end up going to a fake gem store or a crappy tailor or massage parlour, or worse. The tuk-tuk driver will say that he will get a coupon for petrol from the shop if he brings you to their shop and assure you that if you don't want to buy, it is ok. If you take pity on him and agree to go into the shop, you may regret it. 

So far, the Thai government has not taken any action on these people and schemes, so your best bet is to walk away from these touts.