Like motorcycle taxis, tuk tuks are usually used by residents for short distances. When you know the price locals pay, you will be amazed at what they try to extract from foreigners. Usually you would not hire these for long distances. Requests to go long distance are an immediate signal to the driver to over charge as this is not their usual use by residents who know to use meter taxis or other conveyance for longer distances.
Many tuk tuk drivers make much of their money by taking tourists to a gem store, tailor shop, restaurant or the like where they get commissions for taking you there). They are very personable and they have an answer ready for any doubt you might have. This can be OK if you have the time and funds to throw away in the name of “experience” and need some overpriced custom shirts or jewlelry but otherwise you should avoid such trips.
With tuk tuk’s, visitors must negotiate the price before getting in. Trips with tuk tuk offers of over 50 baht should probably be taken by taxi or other conveyance. Clarify on the map they will have handy as to where you want to go; to and make them hold to their bargain, before paying (when you exit the tuk tuk at the end of your trip).