Some thai people try to fool you when you are closed to main touristic areas (such as Grand Palace). They are asking you since how long you arrived in the city. If you say today or yesterday, you are the perfect target because you don't know yet the value of money there. They offer to help you and to give you good and non-touristic prices, but they are lying. Sometime, they are even saying that the place you want to visit is closed, but they have good plans instead. Of course, that's not true.