"It's shut today"
Wherever you ask a tuk-tuk driver to take you, they will tell it's not open, it's open later/tomorrow or its no good. Even outside the Grand Palace where i could see heaps of people going in a tuk-tuk man tried to tell me it was shut! Then they will try to persuade you that they can give you a much better experience. This experience will include at least an hour and a half of your precious time being sucked up in tailors, porcelain shops, carpet shops etc. who are their "sponsors". if you want a tailored suit/porcelain/carpet that's; fine but if not galvanise yourself and give them a firm no, you can always get someone else to take you where you want to go.
